Booster pump and low-temperature-fluid storage tank having the same

ABSTRACT

A low-temperature-fluid storage tank capable of efficiently increasing the pressure of fluid without heating the fluid is provided. There is provided a booster pump which includes a piston having a piston head and a piston rod and a cylinder having a compression chamber that accommodates the piston head so that a fluid is compressed by one end surface of the piston head. The piston head is provided with a bellows for separating a space adjacent to the piston rod from a space adjacent to the cylinder in the compression chamber.

TECHNICAL FIELD

The present invention relates to a booster pump for compressinglow-temperature fluids to increase the pressure and to alow-temperature-fluid storage tank having the same.

BACKGROUND ART

Some known (low-temperature-fluid) booster pumps for compressinglow-temperature (e.g., −273° C. to 0° C.) fluids (e.g., hydrogen,nitrogen, LNG) to increase the pressure have piston rings on pistonheads thereof (refer to, for example, non-Patent Document 1).

Non-patent Document 1:

Takuya Endo et al., “Shin Enerugii Jidousha (New Energy Automobile),”Sankaido, January 1995, p. 221-222

DISCLOSURE OF INVENTION

However, such a known (low-temperature-fluid) booster pump has a problemin that a sliding motion occurs while the outer circumferential surfacesof the piston rings are being pressed onto the inner circumferentialsurface of a cylinder in order to maintain hermeticity, andconsequently, friction between these piston rings and the cylindergenerates heat, which warms up the fluid. Another problem is that,particularly when high pressure is to be achieved, a high-pressure fluidflowing towards the inner circumferential surfaces of the piston ringseven more forcibly presses the outer circumferential surfaces of thepiston rings onto the inner circumferential surface of the cylinder,which produces still more considerable friction between these pistonrings and the cylinder and consequently generates a larger amount ofheat.

In addition, it is not possible to completely eliminate gaps between theouter circumferential surfaces of the piston rings and the innercircumferential surface of the cylinder, and therefore, fluid leaksthrough these gaps, thus causing the compression efficiency to decrease.

Furthermore, such a known (low-temperature-fluid) booster pump requiresa piston rod disposed between a piston head and a drive mechanism tohave a large diameter in order to prevent this piston rod from bucklingdue to compressive force when a low-temperature fluid is to becompressed. For this reason, heat originating from the drive mechanismis transmitted to low-temperature fluid via the piston rod and thepiston head, thereby warming up the low-temperature fluid soconsiderably as to cause boil-off.

The present invention has been conceived in light of the above-describedcircumstances, and an object of the present invention is to provide abooster pump for increasing the pressure of a fluid efficiently withoutheating the fluid and to provide a low-temperature-fluid storage tankhaving such a booster pump.

To overcome the above-described problems, the present invention employsthe following solutions.

The present invention provides a booster pump which includes a pistonhaving a piston head and a piston rod and a cylinder having acompression chamber that accommodates the piston head so that a fluid iscompressed by one end surface of the piston head, wherein the pistonhead is provided with a bellows for separating a space adjacent to thepiston rod from a space adjacent to the cylinder in the compressionchamber.

According to the present invention, the bellows separates a spaceadjacent to the piston rod from a space adjacent to the cylinder in thecompression chamber, and there is no component (e.g., piston ring in theknown art) that moves in contact with the inner circumferential surfaceof the compression chamber. This prevents heat from being generated inthe compression chamber and therefore prevents the fluid from beingheated.

In addition, since the bellows completely separates a space adjacent tothe piston rod from a space adjacent to the cylinder in the compressionchamber, the fluid is prevented from leaking from the cylinder side ofthe compression chamber to the piston rod side of the compressionchamber. This improves the pump efficiency.

In the above-described invention, it is preferable that a filler fillinga space between an outer surface of the bellows and an innercircumferential surface of the cylinder be provided.

By doing so, the gap between the outer surface of the bellows and theinner circumferential surface of the compression chamber is filled, andthe dead volume of the compression chamber decreases. This improves thepump efficiency.

In the above-described invention, it is preferable that a ring-shapedsealing member be provided at one end portion, adjacent to the pistonhead, of the bellows.

By doing so, the sealing member can reduce leakage of the fluid from oneend surface towards the other end surface of the piston head, whichwould reduce the pressure applied to the outer circumferential surfaceof the bellows. This allows a low-pressure bellows which does not needto meet strict robust design requirements to be employed and thereforeallows the piston to have a large stroke. Consequently, the compressionefficiency (pump efficiency) can be improved.

This sealing member neither has tension, as has been problematic, forexample, with a piston ring in the known art, nor generates heat, aswith a piston ring, because the bellows considerably restricts thestroke of the piston (the stroke is small).

In the above-described invention, it is preferable that the piston rodhave a heat-insulating vacuum structure that is hollow and vacuumed.

As a result of the piston rod having a hollow structure, the weight ofthe piston rod can be reduced so that the piston can be pushed up undera small load. In addition, by vacuuming the interior of the piston rod,the piston rod can block heat to reduce the amount of heat propagatingfrom the piston rod into the fluid.

The present invention provides a booster pump which includes at leasttwo of the above-described booster pumps, wherein multistage compressionis performed with these booster pumps.

According to the present invention, if, for example, two booster pumpsare provided, one booster pump can be used as a low-pressure pump andthe other can be used as a high-pressure pump. By doing so, since thelow-pressure pump can employ a low-pressure bellows, the piston can havea large stroke to easily increase the pressure of the fluid from a lowpressure to an intermediate pressure. Furthermore, since thehigh-pressure pump can employ a high-pressure bellows, the intermediatepressure of the fluid can easily be increased to a high pressure, eventhough the piston cannot have a large stroke.

In other words, if the pressure of the fluid is to be increased from lowpressure to high pressure in one stroke using only one booster pump, thehigh-pressure bellows needs to be employed, which does not allow a largestroke. This makes it difficult to increase the fluid to the desiredpressure (high pressure).

In contrast, as described above, the fluid can easily be increased tothe desired pressure by carrying out dual-stage compression of the fluidusing, for example, two pumps.

The present invention provides a low-temperature-fluid storage tank forstoring a low-temperature fluid in a low-temperature state. Thelow-temperature-fluid storage tank includes the above-described boosterpump or the above-described booster; a low-temperature-fluid reservoirreserving the low-temperature fluid; and a low-temperature container foraccommodating the booster pump or the booster and thelow-temperature-fluid reservoir.

According to the present invention, since the booster pump or thebooster is disposed in the low-temperature container, the booster pumpor the booster is forcibly cooled and is not easily heated up.

In the above-described invention, it is preferable that the booster pumpor the booster be disposed downstream of the low-temperature-fluidreservoir and outside the low-temperature-fluid reservoir.

Since the booster pump or the booster is disposed outside thelow-temperature-fluid reservoir (i.e., separately from thelow-temperature-fluid reservoir in the heat-insulated vacuum chamber ofthe low-temperature container), heat generated in a driving source ofthe booster pump or the booster is prevented from being transmitted tothe low-temperature fluid reserved in the low-temperature-fluidreservoir, and therefore, temperature increase and vaporization of thelow-temperature fluid can be prevented.

In the above-described invention, it is preferable that alow-temperature slush fluid in a solid/liquid two-phase state bereserved in the low-temperature-fluid reservoir.

The low-temperature-fluid storage layer contains the slushylow-temperature fluid (mixture of solid low-temperature fluid and liquidlow-temperature fluid in a liquid/ice state) and experiencesvaporization less easily than tanks containing only liquidlow-temperature fluids. This improves the suction performance of thebooster pump or the booster and therefore increases the amount oflow-temperature fluid supplied.

In the above-described invention, it is preferable that a mesh beprovided at an outlet of the low-temperature-fluid reservoir.

Solid low-temperature fluid of the slush fluid is captured by the mesh,and therefore, only liquid low-temperature fluid is supplied to thebooster pump or the booster downstream of the low-temperature-fluidreservoir. This prevents the booster pump or the booster from clogging.

In the above-described invention, it is preferable that a heater beprovided in the low-temperature-fluid reservoir.

By doing so, the solid low-temperature fluid in thelow-temperature-fluid reservoir is heated by the heater into a liquidlow-temperature fluid, which then passes though the mesh up to thebooster pump or the booster.

In the above-described invention, it is preferable that a heat exchangerbe disposed downstream of the booster pump or the booster.

By doing so, the low-temperature fluid that has passed through thebooster pump or the booster by the heat exchanger is vaporized by theheat exchanger and is then supplied to, for example, an engine disposeddownstream for smooth consumption in the engine.

In the above-described invention, it is preferable that a radiationshield plate be provided on an inner surface of the low-temperaturecontainer.

By doing so, the radiation shield plate prevents heat from beingtransmitted from the outside to the inside of the low-temperaturecontainer. This prevents an increase in the temperature of theheat-insulating vacuum layer in the low-temperature container.

The present invention provides a low-temperature-fluid boosting pumpwhich includes a cylinder block having therein a compression chamber;and a piston head that is accommodated in the compression chamber andreciprocates in the compression chamber so that a low-temperature fluidis compressed by one end surface of the piston head, wherein a flexiblepartition for separating a space adjacent to an inner circumferentialside from a space adjacent to an outer circumferential side of thepiston head is provided between the one end surface of the piston headand an inner surface of the compression chamber which faces the one endsurface.

According to the present invention, as a result of the piston headmoving in one direction, a low-temperature fluid is drawn into (suppliedto) the inner space (i.e., the space formed by the one end surface ofthe piston head, the inner circumferential surface of the partition, andthe inner surface of the compression chamber) of the partition. Then, asa result of the piston head moving in the other direction, thelow-temperature fluid is compressed (pressure-boosted) to apredetermined pressure.

More specifically, there are no components (e.g., piston rings in theknown art) that move in contact with each other between the piston headand the inner circumferential surface of the compression chamber andbetween the partition and the inner circumferential surface of thecompression chamber. This prevents heat from being generated in thecompression chamber and therefore prevents the low-temperature fluidfrom being heated.

In addition, the partition completely partitions the innercircumferential side (inward position in the radial direction) from theouter circumferential side (outward position in the radial direction) ofthe compression chamber. Therefore, low-temperature fluid can beprevented from leaking from the inner circumferential side of thecompression chamber to the outer circumferential side of the compressionchamber (or from the outer circumferential side of the compressionchamber to the inner circumferential side of the compression chamber).This improves the compression efficiency of the low-temperature-fluidboosting pump.

In the above-described invention, it is preferable that apressure-boosted fluid reside on an outer side of the partition.

For example, a vaporized low-temperature fluid having a predeterminedpressure is provided (supplied) to an outer side of the partition, andthe pressure difference between the inner side and the outer side of thepartition becomes small (becomes closer).

More specifically, for example, a low-temperature fluid that has beenvaporized as a result of being heated by the heat exchanger andsubjected to pressure adjustment by the pressure regulator to apredetermined pressure (e.g., a pressure half the pressure-boostingforce of the present booster pump) exists on the outer side (towards theoutside in the radial direction) of the partition. Because of this,deformation of the partition can be prevented when the low-temperaturefluid drawn into the inner space of the partition is to be compressed,and therefore, the service life of the partition can be extended. Thisimproves the reliability of the low-temperature-fluid boosting pump.

In the above-described invention, it is preferable that an outer side ofthe partition be vacuumed.

In other words, the space between the partition and the cylinder blockis vacuumed so that the heat on an inner side of the partition (i.e.,heat of the low-temperature fluid compressed on the inner side of thepartition) is prevented from being transmitted to the cylinder block.

By doing so, not only is an increase in the temperature of the cylinderblock suppressed, but also an increase in the temperature of thelow-temperature fluid flowing into the compression chamber issuppressed.

The present invention provides a low-temperature-fluid boosting pumpwhich includes a piston rod driven by a drive unit connected to adriving source; a piston head that is connected to the piston rod andreciprocates with the piston rod; and a cylinder having a compressionchamber that accommodates the piston head so that a low-temperaturefluid is compressed by one end surface of the piston head, wherein thedrive unit is disposed adjacent to the one end surface of the pistonhead, and a shank of the piston rod is subjected to a tensile force in adirection substantially equal to a direction in which the shank extendswhen the low-temperature fluid is to be compressed.

According to the present invention, as a result of the piston rod beingpulled towards the drive unit, the low-temperature fluid is compressedby one end surface of the piston head. In other words, when thelow-temperature fluid is to be compressed, no compressive force isapplied to the piston rod.

As a result, the diameter of the piston rod can be reduced compared witha piston rod in the known art, which is subjected to a compressiveforce. Therefore, not only can the amount of heat entering from adriving source be reduced, but also the weight of the piston rod can bereduced. Consequently, the weight of the entire pump can also bereduced.

In addition, since the piston rod is not subjected to a compressiveforce when the low-temperature fluid is to be compressed, the diameterof the piston head can be increased. In other words, for the known pumpwhere a compressive force is applied to the piston rod, the diameter ofthe piston head is limited to, for example, 40 mm to prevent the pistonrod from buckling. For this reason, the known pump required, forexample, five cylinders to achieve a sufficient flow volume oflow-temperature fluid. For the pump according to the present invention,however, the diameter of the piston head can be, for example, 100 mm,and therefore, a sufficient flow volume can be achieved with a singlecylinder.

As a result, for the pump according to the present invention, not onlycan the structure of the pump be simplified, but also the entire pumpcan be made lightweight and compact.

In the above-described invention, it is preferable that the piston headbe divided into at least two concentric subsections to achieve amultistage compression structure where the low-temperature fluid isgradually increased to a desired pressure by sequentially passingthrough the one end surface of the divided piston head.

The piston head is divided into, for example, two subsections, onesubsection disposed towards the outside in the radial direction and theother disposed towards the inside in the radial direction, so that thefirst compression (first-stage compression) is carried out with thesubsection disposed towards the outside in the radial direction and thesecond compression (second-stage compression) is carried out with thesubsection disposed towards the inside in the radial direction. In otherwords, instead of increasing the pressure from a low pressure to a highpressure in one stroke, the low-temperature fluid is temporarilyincreased to an intermediate pressure, which is then increased to adesired pressure (high pressure).

By doing so, the stroke of the piston head can be made small, andtherefore, the size of the entire pump in the longitudinal direction canbe reduced. This contributes to compact design of the pump.

In the above-described invention, it is preferable that a flexiblepartition for separating a space adjacent to the piston rod from a spaceadjacent to the cylinder in the compression chamber be provided adjacentto the one end surface and adjacent to the other end surface of thepiston head.

The partition separates the space adjacent to the piston rod from thespace adjacent to the cylinder in the compression chamber, and there isno component (e.g., piston ring in the known art) that moves in contactwith the inner circumferential surface of the compression chamber. Thisprevents heat from being generated in the compression chamber andtherefore prevents the flow-temperature fluid from being heated.

In addition, since the partition completely separates a space adjacentto the piston rod from a space adjacent to the cylinder in thecompression chamber, the low-temperature fluid is prevented from leakingfrom the cylinder side of the compression chamber to the piston rod sideof the compression chamber. This improves the compression efficiency.

In the above-described invention, it is preferable that a flexiblepartition for separating a space adjacent to the piston rod from a spaceadjacent to the cylinder in the compression chamber be provided adjacentto the other end surface of the piston head.

By doing so, since all the flexible partitions are provided on the sideopposite to the one end surface (compressive surface) of the pistonhead, the length of the pump in the height direction (longitudinaldirection) can be reduced, and therefore, the pump can be made compact.

In addition, since the one end surface (compressive surface) of thepiston head can be utilized to the full extent for compression of thelow-temperature fluid, a larger amount of low-temperature fluid can becompressed at a time. In short, the efficiency (performance) of the pumpcan be improved.

In the above-described invention, it is preferable that a precoolinglayer be formed in the cylinder.

By doing so, the entire pump can be cooled sufficiently before the pumpis started. This decreases vaporization (boil-off) of thelow-temperature fluid supplied to the pump.

Furthermore, since this precooling layer also serves as aheat-insulating layer while the pump is being operated, vaporization(boil-off) of the low-temperature fluid can be reduced also while thepump is being operated.

In the above-described invention, it is preferable that the drive unitbe linked to the piston rod via a heat-insulating connection section.

Since the drive unit is linked to the piston rod via, for example,rolling elements (e.g., balls and rollers) in point or line contact,heat can be significantly prevented from being transmitted (entering)from the drive unit (i.e., driving source) to the piston rod (i.e.,piston head).

In the above-described invention, it is preferable that the piston headbe linked to the piston rod via a heat insulator.

Since the piston head is linked to the piston rod via the heatinsulator, even if heat is transmitted (enters) from the drive unit tothe piston rod, heat being transmitted (entering) from the piston rod tothe piston head is blocked by the heat insulator.

In the above-described invention, it is preferable that a guiding memberfor guiding the shank of the piston rod be provided between the cylinderand the piston rod.

The guiding member is provided to prevent the piston rod, the pistonhead, etc., which are housed in the cylinder and reciprocate in thecylinder, from interfering with the inner wall surface (cylinder wall)of the cylinder.

By doing so, reciprocating members such as the piston rod and the pistonhead perform reciprocal movement in the cylinder without wobbling orvibrating. This can prevent such reciprocating members from interferingwith the inner wall surface of the cylinder, and furthermore, allows thereciprocating members to be driven smoothly with minimum driving force.

In the above-described invention, it is preferable that a space betweenthe cylinder and the shank of the piston rod be a vacuum.

In other words, since the space between the cylinder and the piston rodis vacuumed, heat from the piston rod (i.e., heat from the drivingsource to the piston rod) is prevented from being transmitted to thecylinder.

As a result, not only is an increase in the temperature of the cylindersuppressed, but also an increase in the temperature of thelow-temperature fluid flowing into the compression chamber issuppressed.

In the above-described invention, it is preferable that the cylinder beimmersed in low-temperature fluid stored in a low-temperature-fluidstorage tank and be attachable to and detachable from thelow-temperature-fluid storage tank.

By doing so, the exterior of a portion that accommodates portions forcompressing the low-temperature fluid therein, such as the cylinder andthe piston head, is immersed in the low-temperature fluid and is alwaysmaintained in a low-temperature state. Furthermore, the cylinder ismounted on a lower portion (bottom portion) of the low-temperature-fluidstorage tank such that it is easily replaceable.

It is preferable that the drive unit and the cylinder be immersed inlow-temperature fluid stored in a low-temperature-fluid storage tank andbe attachable to and detachable from the low-temperature-fluid storagetank. By doing so, the exterior of the entire pump, including a portionthat accommodates portions for compressing the low-temperature fluidtherein, such as the cylinder and the piston head, is immersed in thelow-temperature fluid and is always maintained in a low-temperaturestate. Furthermore, the low-temperature-fluid boosting pump is mountedon a lower portion (bottom portion) of the low-temperature-fluid storagetank such that it is easily replaceable.

The present invention provides a low-temperature-fluid feeder whichincludes the above-described low-temperature-fluid boosting pump; achamber for reserving a low-temperature fluid whose pressure has beenincreased by the above-described low-temperature-fluid boosting pump;and a fuel injector supplied with the low-temperature fluid from thechamber.

According to the present invention, the low-temperature fluid whosepressure has been increased to a desired pressure by thelow-temperature-fluid boosting pump is temporarily reserved in thechamber disposed downstream of the low-temperature-fluid boosting pumpand then passes through a fuel injector into, for example, a combustionchamber, such as an engine.

In the above-described invention, it is preferable that a booster-fluidfeeding unit for liquefying or vaporizing the low-temperature fluid inthe chamber and supplying the low-temperature fluid into the cylinderdisposed adjacent to the other end surface of the piston head of thelow-temperature-fluid boosting pump be provided.

By doing so, the low-temperature fluid in the chamber (or the fluidgenerated by liquefying or vaporizing the low-temperature fluid in thechamber and decreasing the pressure of the liquefied or vaporized fluidusing, for example, a pressure regulator) is supplied into the cylinderdisposed adjacent to the other end surface of the piston head. Thisdecreases the difference between the pressure on the one end surface(compressive surface) side and the pressure on the other end surfaceside of the piston head, thus allowing a bellows with low pressureresistance to be employed.

In the above-described invention, it is preferable that a booster-fluidfeeding unit for vaporizing the low-temperature fluid in theabove-described chamber in a path to the fuel injector and for supplyingthe low-temperature fluid to the cylinder disposed adjacent to the otherend surface of the piston head of the low-temperature-fluid boostingpump be provided.

By doing so, the low-temperature fluid in the chamber (or the fluidgenerated by or vaporizing the low-temperature fluid in the chamber anddecreasing the pressure of the vaporized fluid using, for example, apressure regulator) is supplied into the cylinder disposed adjacent tothe other end surface of the piston head. This decreases the differencebetween the pressure on the one end surface (compressive surface) sideand the pressure on the other end surface side of the piston head, thusallowing a bellows with low pressure resistance to be employed.

In the above-described invention, it is preferable that the chamber beprovided with a relief valve.

By doing so, if the pressure of the chamber storing the low-temperaturefluid exceeds a predetermined pressure, the relief valve operates toprevent the chamber from being damaged. The low-temperature fluiddischarged from the relief valve returns through, for example, a returnpipe to the suction side of the pump (or a separate fuel battery, if anyfuel battery is provided).

The present invention provides a low-temperature-fluid boosting pumpwhich includes a cylinder block having therein a compression chamber;and a piston head that is accommodated in the compression chamber andreciprocates in the compression chamber so that a low-temperature fluidis compressed by one end surface of the piston head, wherein a flexiblepartition for separating a space adjacent to an inner circumferentialside from a space adjacent to an outer circumferential side in thecompression chamber is provided adjacent to the other end surface of thepiston head.

According to the present invention, as a result of the piston headmoving in one direction, a low-temperature fluid is drawn into (suppliedto) the compression chamber. Then, as a result of the piston head movingin the other direction, the low-temperature fluid is compressed(pressure-boosted) to a predetermined pressure.

More specifically, there are no components (e.g., piston rings in theknown art) that move in contact with each other between the piston headand the inner circumferential surface of the compression chamber andbetween the partition and the inner circumferential surface of thecompression chamber. This prevents heat from being generated in thecompression chamber and therefore prevents the low-temperature fluidfrom being heated.

In addition, the partition completely partitions the innercircumferential side (inward position in the radial direction) from theouter circumferential side (outward position in the radial direction) ofthe compression chamber. Therefore, low-temperature fluid can beprevented from leaking from the inner circumferential side of thecompression chamber to the outer circumferential side of the compressionchamber (or from the outer circumferential side of the compressionchamber to the inner circumferential side of the compression chamber).This improves the compression efficiency of the low-temperature-fluidboosting pump.

In the above-described invention, it is preferable that apressure-boosted fluid reside on an inner side of the partition.

For example, a vaporized low-temperature fluid having a predeterminedpressure is provided at (supplied to) an inner side of the partition,and the pressure difference between the inner side and the outer side ofthe partition becomes small (becomes closer).

More specifically, for example, a low-temperature fluid that has beenvaporized as a result of being heated by the heat exchanger andsubjected to pressure adjustment by the pressure regulator to apredetermined pressure (e.g., a pressure half the pressure-boostingforce of the present booster pump) exists on the inner side (towards theinside in the radial direction) of the partition. Because of this,deformation of the partition can be prevented when the low-temperaturefluid drawn into the compression chamber is to be compressed, andtherefore, the service life of the partition can be extended. Thisimproves the reliability of the low-temperature-fluid boosting pump.

In the above-described invention, it is preferable that an inner side ofthe partition be vacuumed.

By doing so, even if, for example, a piston rod linked to the pistonhead is provided on the inner side of the partition, heat from thispiston rod (e.g., heat being transmitted from the driving source to thepiston rod) is prevented from being transmitted to the outer side of thepartition.

As a result, not only is an increase in the temperature of the cylinderblock disposed on the outer side of the partition suppressed, but alsoan increase in the temperature of the low-temperature fluid flowing intothe compression chamber is suppressed.

In the above-described invention, it is preferable that a guiding memberfor guiding the piston head be provided between the cylinder block andthe piston head.

The guiding member is provided to prevent the piston rod, the pistonhead, etc., which are housed in the cylinder and reciprocate in thecylinder, from interfering with the inner wall surface (cylinder wall)of the cylinder.

By doing so, reciprocating members such as the piston rod and the pistonhead perform reciprocal movement in the cylinder without wobbling orvibrating. This can prevent such reciprocating members from interferingwith the inner wall surface of the cylinder, and furthermore, allows thereciprocating members to be driven smoothly with minimum driving force.

In the above-described invention, it is preferable that the cylinderblock be immersed in low-temperature fluid stored in alow-temperature-fluid storage tank and be attachable to and detachablefrom the low-temperature-fluid storage tank.

By doing so, the exterior of a portion that accommodates portions forcompressing the low-temperature fluid therein, such as the cylinderblock and the piston head, is immersed in the low-temperature fluid andis always maintained in a low-temperature state. Furthermore, thecylinder block is mounted on a lower portion (bottom portion) of thelow-temperature-fluid storage tank such that it is easily replaceable.

The present invention affords an advantage in that the pressure of fluidcan be increased efficiently without heating the fluid.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic longitudinal sectional view of a first embodimentof a booster pump according to the present invention.

FIG. 2 is a magnified and simplified cross-sectional view of a main partshown in FIG. 1.

FIG. 3 is a magnified cross-sectional view of a main part of a secondembodiment of a booster pump according to the present invention.

FIG. 4 is a magnified cross-sectional view of a main part of a thirdembodiment of a booster pump according to the present invention.

FIG. 5 is a magnified cross-sectional view of a main part of a fourthembodiment of a booster pump according to the present invention.

FIG. 6 is a magnified cross-sectional view of a main part of a fifthembodiment of a booster pump according to the present invention.

FIG. 7 is a schematic diagram of a main part of one embodiment of abooster according to the present invention.

FIG. 8 is a graph illustrating dual-stage compression achieved using thebooster shown in FIG. 7.

FIG. 9 is a schematic diagram depicting one embodiment of alow-temperature-fluid storage tank according to the present invention.

FIG. 10 is a schematic diagram depicting another embodiment of alow-temperature-fluid storage tank according to the present invention.

FIG. 11 is a schematic longitudinal sectional view of a sixth embodimentof a low-temperature-fluid boosting pump according to the presentinvention.

FIG. 12 is a cross-sectional view taken along line XII-XII of FIG. 11.

FIG. 13 is a schematic longitudinal sectional view of a seventhembodiment of a low-temperature-fluid boosting pump according to thepresent invention.

FIG. 14 is a schematic longitudinal sectional view of an eighthembodiment of a low-temperature-fluid boosting pump according to thepresent invention.

FIG. 15 is a cross-sectional view taken along line XV-XV of FIG. 14.

FIG. 16 is a magnified longitudinal sectional view of a main part of aninth embodiment of a low-temperature-fluid boosting pump according tothe present invention.

FIG. 17 is a schematic longitudinal sectional view of a tenth embodimentof a low-temperature-fluid boosting pump according to the presentinvention.

FIG. 18 is a schematic longitudinal sectional view of an eleventhembodiment of a low-temperature-fluid boosting pump according to thepresent invention.

FIG. 19 is a schematic longitudinal sectional view of a twelfthembodiment of a low-temperature-fluid boosting pump according to thepresent invention.

FIG. 20 is a schematic longitudinal sectional view of a thirteenthembodiment of a low-temperature-fluid boosting pump according to thepresent invention.

FIG. 21 is a schematic longitudinal sectional view of a fourteenthembodiment of a low-temperature-fluid boosting pump according to thepresent invention.

FIG. 22 is a magnified longitudinal sectional view of another embodimentof a bellows applied to a low-temperature-fluid boosting pump accordingto the present invention.

FIG. 23 is a magnified longitudinal sectional view of another embodimentof a heat-insulating connection section applied to alow-temperature-fluid boosting pump according to the present invention.

FIG. 24 is a schematic longitudinal sectional view illustrating afifteenth embodiment of a low-temperature-fluid boosting pump accordingto the present invention.

FIG. 25 is across-sectional view taken along line XXV-XXV of FIG. 24.

FIG. 26 is a schematic longitudinal sectional view of a sixteenthembodiment of a low-temperature-fluid boosting pump according to thepresent invention.

BEST MODE FOR CARRYING OUT THE INVENTION

A first embodiment of a (low-temperature-fluid) booster pump accordingto the present invention will now be described with reference to thedrawings.

As shown in FIG. 1, a booster pump 1 according to this embodiment is aso-called swash-plate (or swash) booster pump. The booster pump 1includes major components such as a plurality of (e.g., seven) pistons11; a cylinder block 12; a cylinder head 13; a drive shaft 14; and aswash plate (also called a “yoke”) 15.

Each piston 11 is a substantially rod-like member which has a circularcross-section. Each piston 11 has a piston head 11 a on one end portionthereof and a piston shoe 11 b on the other end portion thereof. Each ofthe pistons 11 is reciprocably housed in a cylinder 12 a, which will bedescribed later.

The piston head 11 a is a so-called large-diameter portion that has anouter diameter larger than the outer diameter of a piston rod 11 c thatlinks this piston head 11 a and the piston shoe 11 b. A low-temperaturefluid (e.g., liquid hydrogen, liquid nitrogen, liquefied carbon dioxide,liquefied natural gas, or liquefied propane gas) is compressed by oneflat end surface (upper end surface in FIG. 1) of this piston head 11 a.

Like the piston head 11 a, the piston shoe 11 b is also a so-calledlarge-diameter portion that has an outer diameter larger than the outerdiameter of the piston rod 11 c. The piston shoe 11 b is partiallyinterposed, on an end-surface side thereof, between a shoe plate 15 aand a retainer ring 15 b of the swash plate 15, which will be describedlater. Furthermore, the end surface of the piston shoe 11 b slides alonga tilt angle of the swash plate 15 (a sliding surface P of a thrustroller bearing 16 disposed between the shoe plate 15 a and the retainerring 15 b).

The cylinder block 12 has therein the same number of cylinders 12 a asthat of the pistons 11 and the cylinders 12 a are formed in a ring,extending along a longitudinal direction (vertical direction in FIG. 1).Each cylinder 12 a accommodates one piston 11.

A compression chamber 12 b having an inner diameter larger than theouter diameter of the piston head 11 a is provided on one end of eachcylinder 12 a (upper side in FIG. 1) so that this compression chamber 12b accommodates the piston head 11 a.

As shown in FIG. 1 and FIG. 2, which is a magnified view of the mainpart shown in FIG. 1, a bellows 17 is provided in the compressionchamber 12 b.

This bellows 17 partitions (separates) an inner circumferential side(piston 11 side) from an outer circumferential side (cylinder block 12side) of the compression chamber 12 b, which is disposed closer to thepiston shoe 11 b (lower side in FIG. 1) than the piston head 11 a. Oneend surface of the bellows 17 is affixed to a surface opposite (otherend surface) one end surface of the piston head 11 a, and the other endof the bellows 17 is affixed to an inner wall surface of the cylinderblock 12.

Furthermore, this bellows 17 is made of, for example, stainless steel orInconel, which exhibits elasticity at (super) low temperatures.

The cylinder head 13 covers one end surface (upper end surface inFIG. 1) of the cylinder block 12 to close the open ends of the cylinders12 a formed in the cylinder block 12 (i.e., open ends of the compressionchambers 12 b).

On one end surface (lower end surface in FIG. 1) of this cylinder head13, that is, on the surface which faces one end surface of the cylinderblock 12, a suction port 13 a and a discharge port 13 b are provided foreach compression chamber 12 b. Each of the suction port 13 a and thedischarge port 13 b is provided with a ball check valve 18 (a spring isnot shown in the figure for the sake of simplicity) to control suctionand discharge of low-temperature fluid. Furthermore, each suction port13 a communicates with a fluid-suction channel 19 formed in the cylinderhead 13, whereas each discharge port 13 b communicates with afluid-discharge channel 20 formed in the cylinder head 13 and thecylinder block 12. Therefore, low-temperature fluid flowing from thefluid-suction channel 19 through each suction port 13 a to thecompression chamber 12 b is subjected to a pressure increase as a resultof being compressed by one end surface of the piston head 11 a and thengoes out from the discharge port 13 b through the fluid-dischargechannel 20.

The drive shaft 14 transmits a driving force from a driving source(e.g., an electric motor or an engine), not shown in the figure, to theswash plate 15. The drive shaft 14 is rotatably supported at the otherend portion of the cylinder block 12 by bearings 21.

The swash plate 15 includes the shoe plate 15 a and the retainer ring 15b. The sliding surface P of the thrust roller bearing 16 disposedbetween the shoe plate 15 a and the retainer ring 15 b is defined at anangle of, for example, 1.43 degree relative to an axis perpendicular tothe longitudinal axis of the cylinder block 12. Furthermore, theabove-described piston shoe 11 b is partially interposed between theretainer ring 15 b and the thrust roller bearing 16.

On the other hand, a thrust roller bearing 22 is disposed also betweenthe shoe plate 15 and the cylinder block 12. This thrust roller bearing22 provides a thrust (load) in the axial direction (longitudinaldirection of the cylinder block 12).

The shoe plate 15 a, retainer ring 15 b, and thrust roller bearings 16and 22 rotate integrally with the drive shaft 14.

Therefore, when the drive shaft 14 is rotated (in one direction) by thedriving source, the piston shoes 11 b slide along the sliding surface P,and thereby the pistons 11 reciprocate in the cylinder 12, thus causinglow-temperature fluid flowing in the compression chambers 12 b to becompressed successively. In this embodiment, the stroke of each piston11 is set to 2 mm.

Reference numeral 23 in FIG. 1 denotes continuous holes that allow therespective compression chambers 12 b to communicate with the outside ofthe booster pump 1. A pipe 24 is connected to each of these continuousholes 23, and an on-off valve 25 is disposed at an intermediate point inthis pipe 24.

When low-temperature fluid is drawn into each compression chamber 12 b,the continuous hole 23, the pipe 24, and the on-off valve 25 are used tocause low-temperature fluid residing adjacent to the other end surfaceof the piston head 11 a to flow out of the compression chamber 12 b toreduce the drive resistance of the piston 11 or to cause low-temperaturefluid built up in the compression chamber 12 b disposed adjacent to theother end surface of the piston head 11 a to flow out of the compressionchamber 12 b.

Therefore, the on-off valves 25 are closed (off) during a compressionstroke or if it is not necessary to expel low-temperature fluids out ofthe compression chambers 12 b.

The booster pump 1 according to this embodiment does not include acomponent (e.g., piston ring in the known art) that moves in contactwith the inner circumferential surfaces of the compression chambers 12b. This prevents heat from being generated in the compression chambers12 b and therefore prevents the low-temperature fluid from being heated.

Furthermore, the bellows 17 completely separates the innercircumferential side from the outer circumferential side of eachcompression chamber 12 b disposed closer to the piston shoe 11 b thanthe piston head 11 a. This can prevent the low-temperature fluid fromleaking from the outer circumferential side of the compression chamber12 b into the inner circumferential side of the compression chamber 12b. In other words, the low-temperature fluid can be prevented fromflowing out from the compression chamber 12 b side towards the pistonshoe 11 b side along the piston rods 11 c. As a result, the compressionefficiency of the booster pump 1 can be improved.

A second embodiment of a (low-temperature-fluid) booster pump accordingto the present invention will now be described with reference to FIG. 3.

A booster pump 2 in this embodiment differs from the booster pumpaccording to the above-described first embodiment in that (thin) wires(fillers) 31 made of a material that can be used at (super) lowtemperatures, such as Teflon®, is wound around the outer circumferentialsurface of the bellows 17. The other components are the same as thosedescribed in the above-described embodiment, and hence a descriptionthereof will be omitted.

The same components as those in the above-described first embodiment aredenoted with the same reference numerals or symbols.

As shown in FIG. 3, the wires 31 are wound around the outer surface ofthe bellows 17 so as to minimize the gap between the outer surface ofthe bellows 17 and the inner circumferential surface of the compressionchamber 12 b.

Here, care should be exercised to prevent the outer surface of the wires31 wound around the outer surface of the bellows 17 from coming intocontact with the inner circumferential surface of the compressionchamber 12 b, particularly when the piston 11 retracts (goes down inFIG. 1) and the bellows 17 contracts.

According to the booster pump 2 of this embodiment, the gap between theouter surface of the bellows 17 and the inner circumferential surface ofthe compression chamber 12 b is minimized to reduce a dead volume of thecompression chamber 12 b. This increases the compression efficiency.

The other effects and advantages are the same as those of theabove-described first embodiment, and hence a description thereof willbe omitted.

A third embodiment of a (low-temperature-fluid) booster pump accordingto the present invention will now be described with reference to FIG. 4.

A booster pump 3 in this embodiment differs from the booster pumpaccording to the above-described second embodiment in that spacers(fillers) 41 made of a material that can be used at (super) lowtemperatures, such as Teflon®, are provided on the outer circumferentialsurface of the bellows 17. The other components are the same as thosedescribed in the above-described embodiment, and hence a descriptionthereof will be omitted.

The same components as those in the above-described embodiment aredenoted with the same reference numerals or symbols.

As shown in FIG. 4, one spacer 41, which is substantially ring-shaped inplan view, is disposed in each valley (portion recessed towards thepiston rod 11 c, that is, portion further away from the innercircumferential surface of the compression chamber 12 b) of the bellows17 so as to minimize the gap between the outer surface of the bellows 17and the inner circumferential surface of the compression chamber 12 b.This spacer 41 in each valley has a cross section whose shape issubstantially equal to the shape of the cross section of each valley ofthe bellows 17 so as not to prevent the bellows 17 from extending andcontracting.

Here, care should be exercised, as described in the second embodiment,to prevent the outer surface of the spacer 41 disposed in each valley ofthe bellows 17 from coming into contact with the inner circumferentialsurface of the compression chamber 12 b, particularly when the piston 11retracts (goes down in FIG. 1) and the bellows 17 contracts.

Also, according to the booster pump 3 of this embodiment, the gapbetween the outer surface of the bellows 17 and the innercircumferential surface of the compression chamber 12 b is minimized toreduce a dead volume of the compression chamber 12 b. This increases thecompression efficiency.

The other effects and advantages are the same as those of theabove-described first embodiment, and hence a description thereof willbe omitted.

A fourth embodiment of a (low-temperature-fluid) booster pump accordingto the present invention will now be described with reference to FIG. 5.

A booster pump 4 in this embodiment differs from the booster pumpsaccording to the above-described second and third embodiments in thatparticulate filler 51 made of a material that can be used at (super) lowtemperatures, such as Teflon®, is disposed on or near the outercircumferential surface of the bellows 17. The other components are thesame as those described in the above-described embodiments, and hence adescription thereof will be omitted.

The same components as those in the above-described embodiments aredenoted with the same reference numerals or symbols.

As shown in FIG. 5, the particulate filler 51 is disposed between theouter surface of the bellows 17 and the inner circumferential surface ofthe compression chamber 12 b so as to minimize the gap between the outersurface of the bellows 17 and the inner circumferential surface of thecompression chamber 12 b.

Furthermore, an anti-flow ring 52 is provided at one end portion of thebellows 17 to prevent the filler 51 from flowing towards one end surfaceof the piston head 11 a. This ring 52 is formed so as to have an outerdiameter that is smaller than the inner diameter of the compressionchamber 12 b. This prevents the outer circumferential surface of thering 52 from sliding along the inner circumferential surface of thecompression chamber 12 b.

Particles constituting the filler 51 are each formed so as to have anouter diameter larger than the size of the gap between the outercircumferential surface of the ring 52 and the inner circumferentialsurface of the compression chamber 12 b. Furthermore, as much filler 51as necessary is supplied so long as it does not prevent the bellows 17from extending and contracting.

Also, according to the booster pump 4 of this embodiment, the gapbetween the outer surface of the bellows 17 and the innercircumferential surface of the compression chamber 12 b is minimized toreduce a dead volume of the compression chamber 12 b. This increases thecompression efficiency.

The other effects and advantages are the same as those of theabove-described first embodiment, and hence a description thereof willbe omitted.

A fifth embodiment of a (low-temperature-fluid) booster pump accordingto the present invention will now be described with reference to FIG. 6.

A booster pump 5 in this embodiment differs from the booster pumpaccording to the above-described embodiment in that a sealing member 61made of a material that can be used at (super) low temperatures, such asTeflon®, is affixed at one end portion on the outer circumferentialsurface of the bellows 17. The other components are the same as thosedescribed in the above-described embodiment, and hence a descriptionthereof will be omitted.

The same components as those in the above-described embodiment aredenoted with the same reference numerals or symbols.

As shown in FIG. 6, the sealing member 61 for reducing the pressureapplied by the low-temperature fluid to the outer circumferentialsurface of the bellows 17 is disposed at one end portion of the bellows17. This sealing member 61 is formed so as to have an outer diameterthat is substantially equal to the inner diameter of the compressionchamber 12 b so that the outer circumferential surface of the ring 52moves along in slight contact with the inner circumferential surface ofthe compression chamber 12 b. This sealing member 61 neither hastension, as has been problematic, for example, with a piston ring in theknown art, nor generates heat, as with a known piston ring, because thebellows 17 considerably restricts the stroke of the piston 11 (thestroke is small).

In addition, low-temperature fluid built up in the compression chamber12 b disposed adjacent to the other end surface of the piston head 11 aare stored temporarily in a buffer (chamber), not shown in the figure,through the above-described continuous hole 23, pipe 24, and on-offvalve 25 and are then vaporized for use. Alternatively, thislow-temperature fluid returns through a pipe, not shown in the figure,to the fluid-suction channel 19 of the booster pump 5 for the purpose ofrecompression.

According to the booster pump 5 of this embodiment, the sealing member61 can reduce leakage of the low-temperature fluid from one end surfacetowards the other end surface of the piston head 11 a, which wouldreduce the pressure applied to the outer circumferential surface of thebellows 17. This allows a low-pressure bellows which does not need tomeet strict robust design requirements to be employed and thereforeallows the piston 11 to have a large stroke. Consequently, thecompression efficiency (pump efficiency) can be improved.

Furthermore, since the outer circumferential surface of the sealingmember 61 is designed to move along in slight contact with the innercircumferential surface of the compression chamber 12 b, heat generationin the compression chamber 12 b can be reduced significantly.Consequently, heating of the low-temperature fluid can also bemoderated.

The other effects and advantages are the same as those of theabove-described first embodiment, and hence a description thereof willbe omitted.

A (low-temperature-fluid) booster 6 including one of the above-described(low-temperature-fluid) booster pumps as a low-pressure pump 6L and oneof the above-described (low-temperature-fluid) booster pumps as ahigh-pressure pump 6H will be described below with reference to FIGS. 7and 8.

The low-pressure pump 6L compresses low-pressure (low bulk modulus)low-temperature fluid to an intermediate pressure. The low-pressure pump6L includes a low-pressure bellows 17 a which does not need to meetstrict robust design requirements so long as it can withstandintermediate pressure.

On the other hand, the high-pressure pump 6H compresses to high pressurethe intermediate-pressure (high bulk modulus) low-temperature fluidcompressed by the low-pressure pump 6L. The high-pressure pump 6Hincludes a high-pressure bellows 17 b which meets strict robust designrequirements so as to withstand high pressure.

According to this booster 6, since the low-pressure pump 6L employs thelow-pressure bellows 17 a, the piston 11 can have a large stroke toeasily increase the pressure of the low-temperature fluid to anintermediate pressure. Furthermore, since the high-pressure pump 6Hemploys the high-pressure bellows 17 b, the intermediate pressure of thelow-temperature fluid can easily be increased to a high pressure, eventhough the piston 11 cannot have a large stroke in the high-pressurepump 6H.

In other words, if the pressure of low-temperature fluid is to beincreased from low pressure to high pressure in one stroke using onlyone booster pump, the high-pressure bellows 17 b needs to be employed,which does not allow a large stroke. This makes it difficult to increasethe low-temperature fluid to the desired pressure (high pressure).

In contrast, as described above, the low-temperature fluid can beincreased to the desired pressure more easily by carrying out dual-stagecompression of the low-temperature fluid using two pumps.

One embodiment of a low-temperature-fluid storage tank including a(low-temperature-fluid) booster pump or a (low-temperature-fluid)booster will now be described with reference to FIG. 9.

A low-temperature-fluid storage tank 7 in this embodiment includes majorcomponents such as a (low-temperature-fluid) booster pump 71 or a(low-temperature-fluid) booster 72; a low-temperature container 73having therein a heat-insulated vacuum chamber 73 a; alow-temperature-fluid reservoir 74; and a heat exchanger 75.

The booster pump 71 or the booster 72 increases low-temperature fluid toa desired pressure. The booster pump 71 can be realized by, for example,one of the above-described (low-temperature-fluid) booster pumps 1, 2,3, 4, and 5. The booster 72 can be realized by, for example, theabove-described (low-temperature-fluid) booster 6.

The low-temperature container 73 has a vacuum inside and has a radiationshield plate 76, such as a copper plate, affixed to the inner surfacethereof. The above-described booster pump 71 or the booster 72, thelow-temperature-fluid reservoir 74, to be described later, and the heatexchanger 75 are housed in the heat-insulated vacuum chamber 73 a of thelow-temperature container 73.

The low-temperature-fluid storage layer 74 stores therein alow-temperature (e.g., −253° C.) fluid (e.g., liquid hydrogen). Thisstored low-temperature fluid is guided to the low-temperature-fluidboosting pump 71 or the low-temperature-fluid booster 72 through a pipe77.

One end of the heat exchanger 75 is in contact with the inner surface ofthe low-temperature container 73 (i.e., inner surface of the radiationshield plate 76). The heat exchanger 75 exchanges heat with thelow-temperature container 73 to vaporize a low-temperature fluid thathas been subjected to a pressure increase by the booster pump 71 or thebooster 72 and guided through a pipe 78. The low-temperature fluid (gas)vaporized by the heat exchanger 75 is supplied to, for example, anengine through a pipe 79. Furthermore, cool air collected by the heatexchanger 75 is used to cool the above-described radiation shield plate76 or is stored in a regenerating agent, not shown in the figure,provided in the heat-insulated vacuum chamber 73.

According to this low-temperature-fluid storage tank 7, as shown in FIG.9, the booster pump 71 or the booster 72 is disposed in theheat-insulated vacuum chamber 73 a and outside the low-temperature-fluidreservoir 74 (i.e., disposed separated from the low-temperature-fluidreservoir 74 in the heat-insulated vacuum chamber 73 a). Therefore, thebooster pump 71 or the booster 72 is forcibly cooled and is not easilyheated up, and furthermore, heat generated from the driving source canbe prevented from being transmitted to the low-temperature fluidreserved in the low-temperature-fluid reservoir 74. Consequently, anincrease in temperature of the low-temperature fluid can also beprevented.

It is preferable that the booster pump 71 or the booster 72 be cooledsufficiently before being operated.

Another embodiment of a low-temperature-fluid storage tank provided witha (low-temperature-fluid) booster pump or a (low-temperature-fluid)booster will be described below with reference to FIG. 10.

A low-temperature-fluid storage tank 8 in this embodiment includes majorcomponents such as a (low-temperature-fluid) booster pump 81 or a(low-temperature-fluid) booster 82; a low-temperature container 83having therein a heat-insulated vacuum chamber 83 a; alow-temperature-fluid reservoir 84; and a heater 85.

The booster pump 81 or the booster 82 increases low-temperature fluid toa desired pressure. The booster pump 81 can be realized by, for example,one of the above-described (low-temperature-fluid) booster pumps 1, 2,3, 4, and 5. The (low-temperature-fluid) booster 82 can be realized by,for example, the above-described (low-temperature-fluid) booster 6.

The low-temperature container 83 has a vacuum inside and has a radiationshield plate 86, such as a copper plate, affixed to the inner surfacethereof. The above-described booster pump 81 or the booster 82 and thelow-temperature-fluid reservoir 84, to be described later, are housed inthe heat-insulated vacuum chamber 83 a of the low-temperature container83.

The low-temperature-fluid storage layer 84 stores therein alow-temperature (e.g., −260° C.) slushy fluid (e.g., slush hydrogen:mixture of solid hydrogen and liquid hydrogen in a liquid/ice state,with higher density and a higher coldness capacity than liquidhydrogen). This stored low-temperature fluid is guided to thelow-temperature-fluid boosting pump 81 or the low-temperature-fluidbooster 82 through a pipe 87.

If slush hydrogen is stored in the low-temperature-fluid storage layer84, the slush hydrogen is produced by a slush hydrogen producingapparatus, not shown in the figure, provided in thislow-temperature-fluid storage layer 84 or by a slush hydrogen producingfacility 88 separately provided outside the low-temperature container83.

A mesh (screen) 89 is provided in the pipe 86. This mesh 89 is formed soas to pass only liquid low-temperature fluid (e.g., liquid hydrogen)(i.e., so as to block solid hydrogen). By doing so, the booster pump 81or the booster 82 downstream is supplied with only liquidlow-temperature fluid to prevent clogging from occurring in the boosterpump 81 or the booster 82.

The heater 85 changes (melts) solid low-temperature fluid (e.g., solidhydrogen) into liquid low-temperature fluid (e.g., liquid hydrogen).

Furthermore, it is more preferable that the above-described heatexchanger 75 be disposed downstream of the booster pump 81 or thebooster 82 inside (or outside) the low-temperature container 83.

According to this low-temperature-fluid storage tank 8, thelow-temperature-fluid storage layer 84 contains a slushy low-temperaturefluid and experiences vaporization less easily than tanks containingonly liquid low-temperature fluids. This improves the suctionperformance of the booster pump 81 or the booster 82 and thereforeincreases the amount of low-temperature fluid supplied.

Although a dual-stage compression technique using two pumps is employedin the embodiment described with reference to FIGS. 7 and 8, the presentinvention is not limited to this technique. Three-stage compressionusing three pumps or multi-stage compression using three or more pumpscan also be employed.

Furthermore, such multi-stage compression does not always require aplurality of pumps. Instead, multi-stage compression may be achievedwith a single pump.

In addition, the booster pump according to the present invention can beused to increase the pressure of not only low-temperature fluids butalso fluids having various temperatures ranging from normal to hightemperatures.

Furthermore, the piston rods of the booster pump preferably have aheat-insulating vacuum structure that is hollow and vacuumed. As aresult of the piston rods having a hollow structure in this manner, theweight of the piston rods can be reduced so that the pistons can bepushed up under a small load. In addition, by vacuuming the interiors ofthe piston rods, the piston rods can block heat to reduce the amount ofheat propagating from the piston rods into the fluids.

A sixth embodiment of a low-temperature-fluid boosting pump according tothe present invention will be described below with reference todrawings.

As shown in FIG. 11, a low-temperature-fluid boosting pump 101 accordingto this embodiment includes major components such as a drive unit 111and a pump unit 112 driven by this drive unit 111.

The drive unit 111 includes a rod 115 and a power transmission unit 116for transmitting a driving force from a driving source (e.g., anelectric motor or an engine), not shown in the figure, to the rod 115.

The rod 115 is a substantially rod-like member having a circular crosssection, extending downwards from the lower end surface of the powertransmission unit 116. The rod 115 has a heat-insulating connectionsection 128 at a lower end portion thereof.

The power transmission unit 116 causes the rod 115 to reciprocatelinearly in the vertical direction (in the direction indicated by thearrow in FIG. 11) with a stroke of, for example, 2 mm by using a drivingforce from the driving source, not shown in the figure.

The pump unit 112 includes a piston 121, a piston rod 122, and acylinder block 123.

The piston 121 includes one piston main body 124 and one or more (fourin this embodiment) piston heads 125, and is reciprocably housed in acylinder 126 formed in the cylinder block 123.

The piston main body 124 is a substantially disc-shaped member. One endportion of the piston rod 122 is linked to a center portion of thepiston main body 124. In addition, four rods 127 for linking the lowerend surfaces of the respective piston heads 125 to the upper end surfaceof the piston main body 124 are provided on the outer circumference ofthe piston main body 124.

The four piston heads 125 are arranged at regular intervals (90°) asshown in FIG. 12. Each of the piston heads 125 is a substantiallydisc-shaped member and is constructed so as to compress low-temperaturefluids (e.g., liquid hydrogen, liquid nitrogen, liquefied carbondioxide, liquefied natural gas), liquefied propane gases, etc. by meansof one end surface thereof (upper end surface in FIG. 11).

The piston rod 122 is a circular-cross-section, substantially rod-likemember and has one end portion thereof linked to the upper end surfaceof the piston main body 124, as described above, and the other endportion thereof connected to an end portion (lower end portion in FIG.11) of the rod 115 via the heat-insulating connection section 128.

The heat-insulating connection section 128 includes an end portion 128 aof the rod 115 having a structure similar to the inner race of a rollerbearing; the other end portion 128 b of the piston rod 122 having astructure similar to the outer race of a roller bearing; and a pluralityof (four in this embodiment) rolling elements (e.g., balls and rollers)128 c disposed between the end portion 128 a of the rod 115 and theother end portion 128 b of the piston rod 122.

By doing so, the end portion 128 a of the rod 115 and the other endportion 128 b of the piston rod 122 are linked to each other in point orline contact via the rolling elements 128 c. This significantly reducesthe amount of heat transmitted (entering) from the rod 115 to the pistonrod 122.

In addition, since the piston rod 122 is designed to have the maximumpossible length, even if heat is transmitted (enters) from the rod 115to the piston rod 122, the amount of heat transmitted (entering) fromthe piston rod 122 to the piston main body 124 is minimized.

A through-hole 123 a through which the rod 115 passes is formed in thetop center of the cylinder block 123. An inner space 129 communicatingwith the through-hole 123 a is formed inside the top portion of thecylinder block 123. The heat-insulating connection section 128 isaccommodated in this inner space 129.

Furthermore, in the cylinder block 123 below this inner space 129, thecylinder 126 communicating with the inner space 129 via a through-hole123 b through which the piston rod 122 passes is formed in thelongitudinal direction (vertical direction in FIG. 11). One end (upperside in FIG. 11) of the cylinder 126 constitutes compression chambers126 a each having an inner diameter larger than the outer diameter ofthe piston head 125. The piston heads 125 are accommodated in thesecompression chambers 126 a, respectively.

As indicated by reference symbol 123 c, the interiors of the side wall,the bottom surface, and the top surface of the cylinder block 123 arehollow and vacuumed to achieve a heat-insulating vacuum structure.

On the other hand, a suction port 123 d and a discharge port 123 ecommunicating with a compression chamber 126 a are provided at aposition which faces the center of one end surface of the correspondingpiston head 125 in the cylinder block 123, disposed between thecompression chamber 126 a and the inner space 129. The suction port 123d and the discharge port 123 e are each provided with a ball check valve130 to control suction and discharge of low-temperature fluids.

Each suction port 123 d is provided so as to communicate with afluid-suction channel 131 formed in the cylinder block 123, whereas eachdischarge port 123 e is provided so as to communicate with afluid-discharge channel 132 formed in the cylinder block 123. Therefore,a low-temperature fluid guided from the fluid-suction channel 131 viaeach suction port 123 d into the compression chamber 126 a is compressedby one end surface of the piston head 125 so that the pressure isincreased to, for example, 30 MPa. Thereafter, the low-temperature fluidis guided out of the cylinder block 123 from the discharge port 123 evia the fluid-discharge channel 132.

The low-temperature fluid that has been guided out of the cylinder block123 via the fluid-discharge channel 132 is temporarily stored (reserved)in a chamber 134 via a pipe 133. The low-temperature fluid reserved inthe chamber 134 is guided into a heat exchanger 136 through a pipe 135and then vaporized. Most of the low-temperature fluid is supplied to afuel injector, not shown in the figure, through a pipe 137, whereas partof the low-temperature fluid is guided through a pipe 138 and a pressureregulator (decompressor) 139 into the cylinder 126 (a space between thelower surface at the other end portion of the piston main body 124,disposed adjacent to the other end side, i.e., the side opposite to thecompression chambers 126 a, of the cylinder 126, and the bottom surfaceof the cylinder 126).

Low-temperature fluid whose pressure has been increased to, for example,30 MPa is reserved in the chamber 134.

In addition, vaporized low-temperature fluid whose pressure has beendecreased to, for example, 15 MPa by the pressure regulator 139 issupplied into the cylinder 126.

Each compression chamber 126 a has a bellows (partition) 140 therein.This bellows 140 partitions (separates) an inner circumferential side(inward position in the radial direction) from an outer circumferentialside. (outward position in the radial direction) of the correspondingcompression chamber 126 a, which is disposed above the piston head 125(on the opposite side to the piston main body 124). One end of thebellows 140 is affixed to an outer circumferential end portion on oneend surface of the piston head 125, and the other end of the bellows 140is affixed to the inner wall surface of the cylinder block 123 locatedat an outward position in the radial direction of the suction port 123 dand the discharge port 123 e.

Furthermore, a bellows (partition) 141 is also provided at an outwardposition in the radial direction at one end portion of the piston rod122. This bellows 141 partitions (separates) an inner circumferentialside (adjacent to the piston rod 122) from an outer circumferential side(adjacent to the cylinder block 123) of the piston rod 122 at one endportion thereof. One end of the bellows 141 is affixed to the upper endsurface of the piston main body 124, and the other end of the bellows141 is affixed to the inner wall surface of the cylinder block 123.

Furthermore, these bellows 140 and 141 are made of, for example,stainless steel or Inconel, which exhibits elasticity at (super) lowtemperatures.

Reference numerals 142, 143, and 144 in FIG. 11 each denote a(heat-insulating) sealing member which is ring-shaped in plan view.

FIG. 12 is a cross-sectional view taken along line XII-XII of FIG. 11.

With the above-described structure, when the rod 115 of the drive unit111 reciprocates linearly in the vertical direction, the piston rod 122linked to the rod 115 through the heat-insulating connection section 128reciprocates linearly in the vertical direction together with the piston121, low-temperature fluid supplied from the suction ports 123 d iscompressed by one end surface of each piston head 125 so that thepressure is increased, and then the low-temperature fluid is expelledfrom the discharge port 123 e via the fluid-discharge channel 132 to theoutside of the cylinder block 123.

The low-temperature-fluid boosting pump 101 according to this embodimentdoes not include a component (e.g., piston ring in the known art) thatmoves in contact with the inner circumferential surfaces of thecompression chambers 126 a. This prevents heat from being generated inthe compression chambers 126 a and therefore prevents thelow-temperature fluid from being heated.

In addition, each bellows 140 completely partitions an innercircumferential side (inward position in the radial direction) from anouter circumferential side (outward position in the radial direction) ofthe corresponding compression chamber 126 a. Therefore, low-temperaturefluid can be prevented from leaking from the inner circumferential sideof the compression chamber 126 a to the outer circumferential side ofthe compression chamber 126 a (or from the outer circumferential side ofthe compression chamber 126 a to the inner circumferential side of thecompression chamber 126 a). This improves the compression efficiency ofthe low-temperature-fluid boosting pump 101.

Furthermore, since low-temperature fluid that is vaporized by the heatexchanger 136 and subjected to pressure adjustment to a predeterminedpressure (e.g., 15 MPa) by the pressure regulator 139 exists outsideeach bellows 140 (outward position in the radial direction), deformationof the bellows 140 can be reduced when low-temperature fluid drawn intothe bellows 140 is to be compressed. This extends the service life ofthe bellows 140 and increases the reliability of thelow-temperature-fluid boosting pump 101.

In addition, according to the low-temperature-fluid boosting pump 101 ofthis embodiment, since low-temperature fluid is compressed in the innerspace of each bellows 140 (the space defined by the innercircumferential surface of the bellows 140, one end surface of thepiston head 125, and the top surface of the compression chamber 126 a),the length of each rod 127 linking the piston head 125 to the pistonmain body 124 can be reduced. Consequently, not only can the length ofthe pump unit 112 in the longitudinal direction (axial direction) bereduced, but also the length of the entire pump in the longitudinaldirection (axial direction) can be reduced. This contributes to compactand lightweight design of the pump.

Furthermore, as a result of the piston rod 122 being pulled towards thedrive unit 111 (upward in FIG. 11), low-temperature fluid is compressedby one end surface of each piston head 125. In other words, whenlow-temperature fluid is to be compressed, no compressive force isapplied to the piston rod 122.

As a result, the diameter of the piston rod 122 can be reduced comparedwith a piston rod in the known art, which is subjected to a compressiveforce. Therefore, not only can the amount of heat entering from adriving source be reduced, but also the weight of the piston rod 122 canbe reduced. Consequently, the weight of the entire pump can also bereduced.

In addition, the heat-insulating connection section 128 reduces theamount of heat entering from the rod 115 to the piston rod 122, therebyfurther reducing the amount of heat entering from the driving source.

Furthermore, because the piston main body 124 is provided between thepiston rod 122 and the piston heads 125, heat from the piston rod 122reaches the piston heads 125 through the piston main body 124. This canfurther reduce the input amount of heat.

In addition, since the rod 115 connecting to the power transmission unit116 extends to the side where the suction ports 123 d and the dischargeports 123 e are disposed (upper side in FIG. 11), not only can thelength of the pump unit 112 in the longitudinal direction (axialdirection) be reduced, but also the length of the entire pump in thelongitudinal direction (axial direction) can be reduced. Thiscontributes to compact and lightweight design of the pump.

A seventh embodiment of a low-temperature-fluid boosting pump accordingto the present invention will now be described with reference to FIG.13.

A low-temperature-fluid boosting pump 202 according to this embodimentis a so-called swash plate (or swash) pump. The low-temperature-fluidboosting pump 202 includes major components such as a drive unit 261 anda pump unit 262 that is driven by this drive unit 261.

The same components as those in the above-described sixth embodiment aredenoted with the same reference numerals or symbols.

The drive unit 261 includes a rod 265 and a power transmission unit 266that transmits a driving force from a driving source (e.g., an electricmotor or an engine), not shown in the figure, to the rod 265.

The rod 265 is a substantially rod-like member having a circular crosssection, extending downwards from the lower end surface of the powertransmission unit 266.

The power transmission unit 266 rotates the rod 265 in one direction(direction indicated by the arrow in FIG. 13) using a driving force froma driving source, not shown in the figure.

The pump unit 262 includes one or more (four in this embodiment) pistons271, a swash plate (also called a “yoke”) 272, and a cylinder block 273.

Each piston 271 is a circular-cross-section, substantially rod-likemember having a piston head 271 a at one end portion thereof and apiston shoe 271 b at the other end portion thereof. Each piston 271 isreciprocably housed in a cylinder 276.

The piston head 271 a is a so-called large-diameter portion that has anouter diameter larger than the outer diameter of a piston rod 271 c thatlinks this piston head 271 a and the piston shoe 271 b. Low-temperaturefluid (e.g., liquid hydrogen, liquid nitrogen, liquefied carbon dioxide,liquefied natural gas), liquefied propane gas, etc. are compressed byone flat end surface (upper end surface in FIG. 13) of this piston head271 a.

Like the piston head 271 a, the piston shoe 271 b is also a so-calledlarge-diameter portion that has an outer diameter larger than the outerdiameter of the piston rod 271 c. One end surface (lower surface in FIG.13) of the piston shoe 271 b slides along a sliding surface P of theswash plate 272 having a tilt angle.

The cylinder block 273 has therein the same number of compressionchambers 126 a as that of the pistons 271 and the compression chambers126 a are formed along a longitudinal direction (vertical direction inFIG. 13). Each compression chamber 126 a accommodates one piston head271 a.

As shown in FIG. 13, the piston shoes 271 b and the swash plate 272 arehoused adjacent to the other end side (lower side in FIG. 13) of thecylinder 276.

Furthermore, a through-hole 123 a through which the rod 265 passes isformed in the center of the cylinder block 273. Furthermore, theinteriors of the side wall, the bottom surface, and the top surface ofthe cylinder block 123 constitute a heat-insulating vacuum structurethat is hollow and vacuumed, as shown by reference symbol 123 c.

On the other hand, a suction port 123 d and a discharge port 123 ecommunicating with a compression chamber 126 a are provided at aposition which faces the center of one end surface of the correspondingpiston head 271 a, i.e., at a top portion in the cylinder block 273. Thesuction port 123 d and the discharge port 123 e are each provided with aball check valve 130 to control suction and discharge of low-temperaturefluid.

Each suction port 123 d is provided so as to communicate with afluid-suction channel 131 formed in the cylinder block 123, whereas eachdischarge port 123 e is provided so as to communicate with afluid-discharge channel 132 formed in the cylinder block 123. Therefore,low-temperature fluid guided from the fluid-suction channel 131 via eachsuction port 123 d into the compression chamber 126 a is compressed byone end surface of the piston head 271 a so that the pressure isincreased to, for example, 30 MPa. Thereafter, the low-temperature fluidis guided out of the cylinder block 273 from the discharge port 123 evia the fluid-discharge channel 132.

The low-temperature fluid that has been guided out of the cylinder block273 via the fluid-discharge channel 132 is temporarily stored (reserved)in a chamber 134 via a pipe 133. The low-temperature fluid reserved inthe chamber 134 is guided into a heat exchanger 136 through a pipe 135and then vaporized. Most of the low-temperature fluid is supplied to afuel injector, not shown in the figure, through a pipe 137, whereas partof the low-temperature fluid is guided through a pipe 138 and a pressureregulator (decompressor) 139 into the compression chamber 126 a (i.e., aspace adjacent to the other end surface of each piston head 271 a,located opposite to a bellows 140).

Low-temperature fluid whose pressure has been increased to, for example,30 MPa is reserved in the chamber 134.

In addition, vaporized low-temperature fluid whose pressure has beendecreased to, for example, 15 MPa by the pressure regulator 139 issupplied into the compression chamber 126 a.

Each compression chamber 126 a has the bellows (partition) 140 therein.This bellows 140 partitions (separates) an inner circumferential side(inward position in the radial direction) from an outer circumferentialside (outward position in the radial direction) of the correspondingcompression chamber 126 a, which is disposed above the piston head 271 a(on the opposite side to the piston rod 271 c). One end of the bellows140 is affixed to an outer circumferential end portion on one endsurface of the piston head 271 a, and the other end of the bellows 140is affixed to the inner wall surface of the cylinder block 273 locatedat an outward position in the radial direction of the suction port 123 dand the discharge port 123 e.

Furthermore, a bellows (partition) 280 is also provided at an outwardposition in the radial direction at one end portion of the piston rod271 c. This bellows 280 partitions (separates) an inner circumferentialside (adjacent to the piston rod 271 c) from an outer circumferentialside (adjacent to the cylinder block 273) of the piston rod 271 c at oneend portion thereof. One end of the bellows 280 is affixed to an outercircumferential end portion on the other end surface (upper surface inFIG. 13) of the piston shoe 271 b, and the other end of the bellows 280is affixed to the inner wall surface of the cylinder block 273.

These bellows 140 and 280 are made of, for example, stainless steel orInconel, which exhibits elasticity at (super) low temperatures.

Reference numerals 142, 143, and 144 in FIG. 13 each denote a(heat-insulating) sealing member which is ring-shaped in plan view.Reference numerals 281 and 282 each denote a thrust roller bearing.

With the above-described structure, when the rod 265 is rotated by thedriving source (in one direction), the piston shoes 271 b slide alongthe sliding surface P by means of the thrust bearings 281, andfurthermore, the pistons 271 are caused to reciprocate in the cylinder276, thereby successively compressing low-temperature fluid flowing intothe compression chambers 126 a. In this embodiment, the strokes of thepistons 271 are set to, for example, 2 mm.

The low-temperature-fluid boosting pump 202 according to this embodimentdoes not include a component (e.g., piston ring in the known art) thatmoves in contact with the inner circumferential surfaces of thecompression chambers 126 a. This prevents heat from being generated inthe compression chambers 126 a and therefore prevents thelow-temperature fluid from being heated.

In addition, each bellows 140 completely partitions (separates) an innercircumferential side (inward position in the radial direction) from anouter circumferential side (outward position in the radial direction) ofthe corresponding compression chamber 126 a. Therefore, low-temperaturefluid can be prevented from leaking from the inner circumferential sideof the compression chamber 126 a to the outer circumferential side ofthe compression chamber 126 a (or from the outer circumferential side ofthe compression chamber 126 a to the inner circumferential side of thecompression chamber 126 a). This improves the compression efficiency ofthe low-temperature-fluid boosting pump 202.

Furthermore, since low-temperature fluid that is vaporized by the heatexchanger 136 and subjected to pressure adjustment to a predeterminedpressure (e.g., 15 MPa) by the pressure regulator 139 exists outsideeach bellows 140 (outward position in the radial direction), deformationof the bellows 140 can be reduced when low-temperature fluid drawn intothe bellows 140 is to be compressed. This extends the service life ofthe bellows 140 and increases the reliability of thelow-temperature-fluid boosting pump 202.

In addition, according to the low-temperature-fluid boosting pump 202 ofthis embodiment, since low-temperature fluid is compressed in the innerspace of each bellows 140 (the space defined by the innercircumferential surface of the bellows 140, one end surface of thepiston head 271 a, and the top surface of the compression chamber 126a), the length of each piston rod 271 c linking the piston head 271 a tothe piston shoe 271 b can be reduced. Consequently, not only can thelength of the pump unit 262 in the longitudinal direction (axialdirection) be reduced, but also the length of the entire pump in thelongitudinal direction (axial direction) can be reduced. Thiscontributes to compact and lightweight design of the pump.

Furthermore, as a result of the rod 265 being rotated in one direction(as indicated by the arrow in FIG. 13), the low-temperature fluid iscompressed by one end surface of each piston head 271 a. In other words,when the low-temperature fluid is to be compressed, no compressive forceis applied to the rod 265.

As a result, the diameter of the rod 265 can be reduced compared withthe type of piston rod used in the known art, which is subjected to acompressive force. Therefore, not only can the amount of heat enteringfrom a driving source be reduced, but also the weight of the rod 265 canbe reduced. Consequently, the weight of the entire pump can also bereduced.

In addition, since the rod 265 connecting to the power transmission unit266 extends to the side where the suction ports 123 d and the dischargeports 123 e are disposed (upper side in FIG. 13), not only can thelength of the pump unit 262 in the longitudinal direction (axialdirection) be reduced, but also the length of the entire pump in thelongitudinal direction (axial direction) can be reduced. Thiscontributes to compact and lightweight design of the pump.

Although a four-cylinder structure provided with four pistons and fourcylinders has been described in the above-described embodiment, thepresent invention is not limited to this structure. For example, asingle-cylinder, two-cylinder, three-cylinder, or five-or-more-cylinderstructure is also acceptable.

Furthermore, the thrust roller bearing 282 described in the seventhembodiment is not limited to the type of bearing that supports the swashplate 272 at a single point in the center on the bottom surface of theswash plate 272, as shown in FIG. 13. Instead, the entire bottom surfaceof the swash plate 272 can be supported with two or more thrust rollerbearings disposed in the circumferential direction.

In addition, it is preferable that the angle of this swash plate 272 bevariable using, for example, an actuator. In other words, avariable-capacity structure is preferable. By doing so, the amount ofdischarge by the pump can be changed simply by changing the angle of theswash plate 272, i.e., without changing the number of revolutions fordriving the pump.

Furthermore, although each of the suction port 123 d and the dischargeport 123 e is provided with the ball check valve 130 in theabove-described embodiment, the present invention is not limited to thisstructure. Instead, a forcible drive system as seen with, for example, aDOHC of an internal-combustion engine is also acceptable. Furthermore, astructure with a reed valve, a poppet valve, etc. can also be used.

In addition, although low-temperature fluid vaporized by the heatexchanger 136 is supplied to the outside of the bellows 140 and 280 inthe above-described sixth embodiment or the seventh embodiment, thepresent invention is not limited to this structure. Instead, the spacereceiving vaporized low-temperature fluid can be vacuumed.

More specifically, the spaces between the bellows 140 and 280 and thecylinder blocks 123 and 273 are vacuumed to prevent heat in the bellows140 and 280 (i.e., heat of low-temperature fluid compressed at the innersides of the bellows 140 and 280) from being transmitted to the cylinderblocks 123 and 273.

By doing so, not only is an increase in the temperature of the cylinderblocks 123 and 273 suppressed, but also an increase in the temperatureof the low-temperature fluid flowing into the compression chambers issuppressed.

In this case, the pipe 138 and the pressure regulator 139 shown in FIGS.11 and 13 are omitted.

Furthermore, in the above-described sixth embodiment, it is morepreferable that a guiding member be provided, for example, between thepiston rod 122 and the cylinder block 123 or between the linkage member124 and the cylinder 126 so that the piston main body, the piston heads,etc. that are housed in the cylinder to reciprocate in the cylinder donot interfere with the inner wall surface of the cylinder (cylinderwall).

Examples of such a guiding member include a linear bearing disposedbetween the piston rod 122 and the cylinder block 123 or between theouter circumferential surface of the linkage member 124 and the innerwall surface of the cylinder 126, a member that guides a cylindricalprotrusion protruding downwards from the lower end surface of thelinkage member 124 into a cylindrical indentation (dent) formed in thecenter of the bottom surface of cylinder 126, and so forth.

By doing so, reciprocating members such as the piston main body and thepiston heads perform reciprocal movement in the cylinder withoutwobbling or vibrating. This can prevent such reciprocating members frominterfering with the inner wall surface of the cylinder, andfurthermore, allows the reciprocating members to be driven smoothly withminimum driving force.

In addition, in each of the above-described sixth and the seventhembodiments, spaces receiving the low-temperature fluid vaporized inthese embodiments can be vacuumed.

By doing so, not only is an increase in the temperature of the cylinderblocks suppressed, but also an increase in the temperature oflow-temperature fluid flowing into the compression chambers issuppressed.

In this case, the pipe 138 and the pressure regulator 139 shown in FIGS.11 and 13 are omitted.

Furthermore, in the above-described sixth embodiment, it is morepreferable that an vacuumed space be formed between the piston rod 122and the cylinder block 123.

For example, a bellows (same as the bellows 141) for separating a spaceadjacent to the inner circumferential side from a space adjacent to theouter circumferential side of the piston rod 122 is provided between thelower surface of the other end portion 128 b of the piston rod 122 andthe upper surface of the bottom of the inner space 129 shown in FIG. 11.

More specifically, the space between the cylinder block 123 and thepiston rod 122 is vacuumed to prevent heat from the piston rod 122(i.e., heat moving from the drive unit 111 side to the piston rod 122side) from being transmitted to the cylinder block 123.

By doing so, not only is an increase in the temperature of the cylinderblocks 123 suppressed, but also an increase in the temperature oflow-temperature fluid flowing into the compression chambers 126 a issuppressed.

An eighth embodiment of a low-temperature-fluid boosting pump accordingto the present invention will be described with reference to thedrawings.

As shown in FIG. 14, a low-temperature-fluid boosting pump 301 accordingto this embodiment includes major components such as a drive unit 311and a pump unit 312 driven by this drive unit 311.

The drive unit 311 includes a cam 313; a reciprocating section 314; alinear bearing 315; an urging member 316; and a casing 317 foraccommodating these elements.

The cam 313 is a circular arc cam (convex cam) having a maximum lift of,for example, 2 mm and is fixed on a drive shaft 318 of a driving source(e.g., an electric motor or an engine), not shown in the figure. The cam313 rotates in one direction along with the drive shaft 318, whichrotates as a result of the driving source being driven.

The reciprocating section 314 is a substantially cylindrical memberhaving an inner space formed therein. The reciprocating section 314 hasa roller bearing 319 in the inner space thereof, and furthermore, asubstantially bar-like rod 320 having a circular cross section extendsdownwards from the lower end surface of the reciprocating section 314.

The roller bearing 319 includes an inner race (inner ring) 319 a; anouter race (outer ring) 319 b; and a plurality of rolling elements(e.g., balls and rollers) 319 c disposed between the inner race 319 aand the outer race 319 b. The inner race 319 a is affixed to a shaft 314a protruding in the inner space of the reciprocating section 314,whereas the outer race 319 b rotates together with the cam 313 as aresult of the outer surface thereof being in line contact with the outersurface of the rotating cam 313.

The linear bearing 315 guides the outer circumferential surface, at aradially outward position, of the reciprocating section 314 such thatthe reciprocating section 314 reciprocates linearly in the verticaldirection. The linear bearing 315 is affixed to an inner surface of aside wall of the casing 317 at a radially outward position of thereciprocating section 314. A plurality of rolling elements (e.g., ballsand rollers) 315 a is disposed in the linear bearing 315. By doing so,the reciprocating section 314 can perform smooth linear reciprocation inthe vertical direction.

The linear bearing 315 can be made of, for example, resin, titanium, orceramic.

The urging member 316 is affixed to an inner wall surface at the upperportion of the casing 317. The urging member 316 is, for example, acompression spring that is disposed above the reciprocating section 314to urge the reciprocating section 314 downwards, that is, to urge theouter surface of the outer race 319 b of the roller bearing 319 onto theouter surface of the cam 313.

The casing 317 is a substantially cylindrical member having an innerspace therein for accommodating the cam 313, the reciprocating section314, the linear bearing 315, and the urging member 316. The casing 317is disposed above the pump unit 312.

With the above-described structure, as the driving source is driven tocause the cam 313 to rotate along with the drive shaft 318, the rollerbearing 319, whose outer surface is pressed against the outer surface ofthe cam 313, reciprocates linearly in the vertical direction togetherwith the reciprocating section 314. Accordingly, the rod 320 alsoreciprocates in the vertical direction.

The pump unit 312 includes a piston 321, a piston rod 322, and acylinder block 323.

The piston 321 includes a piston main body 324 and a piston head 325 andis reciprocably housed in a cylinder 326 formed in the cylinder block323.

The piston main body 324 is a substantially cup-shaped hollow memberwith a bottom. The piston main body 324 has the piston head 325 formedat one end portion (upper end portion in FIG. 14) thereof and has, inthe center of the other end portion (bottom) thereof, a through-hole 324a through which one end portion of the piston rod 322 passes and one endportion of the piston rod 322 which is mounted via a heat insulator 327.In addition, as indicated by reference symbol 324 b, the interior of theside wall of the piston main body 324 has a heat-insulating vacuumstructure that is hollow and vacuumed.

The piston head 325 is a member which is ring-shaped in plan view(doughnut) and has in the center thereof a through-hole 325 a throughwhich the piston rod 322 and a bulkhead 334, to be described later,pass. A low-temperature fluid (e.g., liquid hydrogen, liquid nitrogen,liquefied carbon dioxide, liquefied natural gas, or liquefied propanegas) is compressed by one flat end surface (upper end surface in FIG.14) of the piston head 325.

The piston rod 322 is a circular-cross-section, substantially rod-likemember and has one end portion thereof affixed to the center at theother end portion of the piston main body 324 via the heat insulator327, as described above, and the other end portion thereof connected toan end portion (lower end portion in FIG. 14) of the rod 320 via aheat-insulating connection section 328.

The heat-insulating connection section 328 includes an end portion 328 aof the rod 320 having a structure similar to the inner race of a rollerbearing; the other end portion 328 b of the piston rod 322 having astructure similar to the outer race of a roller bearing; and a pluralityof (four in this embodiment) rolling elements (e.g., balls and rollers)328 c disposed between the end portion 328 a of the rod 320 and theother end portion 328 b of the piston rod 322.

By doing so, the end portion 328 a of the rod 320 and the other endportion 328 b of the piston rod 322 are linked to each other in point orline contact via the rolling elements 328 c. This significantly reducesthe amount of heat transmitted (entering) from the rod 320 to the pistonrod 322.

In addition, since one end portion of the piston rod 322 is linked tothe center of the other end portion of the piston main body 324 via theheat insulator 327, even if heat is transmitted (enters) from the rod320 to the piston rod 322, heat transmitted (entering) from the pistonrod 322 to the piston main body 324 is blocked by the heat insulator327.

A through-hole 323 a through which the rod 320 passes is formed in thetop center of the cylinder block 323. An inner space 329 communicatingwith the through-hole 323 a is formed inside the top portion of thecylinder block 323. The heat-insulating connection section 328 isaccommodated in this inner space 329.

Furthermore, in the cylinder block 323 disposed below this inner space329, the cylinder 326 communicating with the inner space 329 via athrough-hole 323 b through which the piston rod 322 passes is formed inthe longitudinal direction (vertical direction in FIG. 14). One end(upper side in FIG. 14) of the cylinder 326 constitutes a compressionchamber 126 a having an inner diameter larger than the outer diameter ofthe piston head 325. The piston head 325 is accommodated in thiscompression chamber 326 a.

As indicated by reference symbol 323 c, the interiors of the side wall,the bottom surface, and the top surface of the cylinder block 323 arehollow and vacuumed to achieve a heat-insulating vacuum structure.

On the other hand, a suction port 323 d and a discharge port 323 ecommunicating with the compression chamber 326 a are provided at aposition which faces a circumferential portion on one end surface of thepiston head 325 between the compression chamber 326 a and the innerspace 329 in the cylinder block 323. The suction port 323 d and thedischarge port 323 e are each provided with a poppet check valve (or aball check valve, a reed valve, a forcibly driven valve) 330 having avalve body 330 a and a spring 330 b to control suction and discharge oflow-temperature fluid.

The suction port 323 d is provided so as to communicate with afluid-suction channel 331 formed in the cylinder block 323, whereas thedischarge port 323 e is provided so as to communicate with afluid-discharge channel 332 formed in the cylinder block 323. Therefore,low-temperature fluid guided from the fluid-suction channel 331 via thesuction port 323 d into the compression chamber 326 a is compressed byone end surface of the piston head 325 so that the pressure is increasedto, for example, 30 MPa. Thereafter, the low-temperature fluid is guidedout of the cylinder block 323 from the discharge port 323 e via thefluid-discharge channel 332.

The low-temperature fluid that has been guided out of the cylinder block323 via the fluid-discharge channel 332 is temporarily stored (reserved)in a chamber C via a pipe 333. Thereafter, the low-temperature fluid issupplied to a fuel injector, not shown in the figure, via a pipe 335.

Low-temperature fluid whose pressure has been increased to, for example,30 MPa is reserved in the chamber C.

The bulkhead 334 enclosing the shank outer surface of the piston rod 322is disposed between the piston rod 322 and the piston 321. As indicatedby reference symbol 334 a, this bulkhead 334 has a heat-insulatingvacuum structure that is hollow and vacuumed. Because of this, radiantheat from the piston rod 322 is prevented from being transmitted to thepiston 321.

The compression chamber 326 a has a bellows (partition) 336 therein.This bellows 336 separates (partitions) an inner circumferential side(piston 321 side) from an outer circumferential side (cylinder block 323side) of the compression chamber 326 a, which is disposed closer to thepiston main body 324 (lower side in FIG. 14) than the piston head 325.One end of the bellows 336 is affixed to a surface opposite (the otherend surface) one end surface of the piston head 325, and the other endof the bellows 336 is affixed to the inner wall surface of the cylinderblock 323.

A bellows (partition) 337 is also provided at a radially outwardposition of the bulkhead 334 and above one end surface of the pistonhead 325. This bellows 337 separates (partitions) an innercircumferential side (piston rod 322 side) from an outer circumferentialside (cylinder block 323 side) in the upper section of the cylinder 326.One end of the bellows 337 is affixed to one end surface of the pistonhead 325, whereas the other end of the bellows 337 is affixed to theinner wall surface of the cylinder block 323.

Furthermore, these bellows 336 and 337 are each made of, for example,stainless steel or Inconel, which exhibits elasticity at (super) lowtemperatures.

FIG. 15 is a cross-sectional view taken along line XV-XV of FIG. 14. Theimaginary line in FIG. 15 (two-dot chain line) denotes the bellows 337.

Furthermore, reference numerals 338, 339, 340, and 341 in FIG. 14 eachdenote a (heat-insulating) sealing member which is ring-shaped in planview.

With the above-described structure, when the rod 320 of the drive unit311 reciprocates linearly in the vertical direction, the piston rod 322linked to the rod 320 through the heat-insulating connection section 328reciprocates linearly in the vertical direction together with the piston321, low-temperature fluid supplied from the suction port 323 d iscompressed by one end surface of the piston head 325 so that thepressure is increased, and then the low-temperature fluid is expelledfrom the discharge port 323 e via the fluid-discharge channel 332 to theoutside of the cylinder block 323.

According to the low-temperature-fluid boosting pump 301 of thisembodiment, as a result of the piston rod 322 being pulled towards thedrive unit 311 (upwards in FIG. 14), low-temperature fluid is compressedby one end surface of the piston head 325. In short, whenlow-temperature fluid is to be compressed, the piston rod 322 is notsubjected to a compressive force.

As a result, the diameter of the piston rod 322 can be reduced comparedwith a piston rod in the known art, which is subjected to a compressiveforce (if the piston rod 322 is made of, for example, Inconel, thediameter of the piston rod 322 can be, for example, 8 mm). Therefore,not only can the amount of heat entering from the driving source bereduced, but also the weight of the piston rod 322 can be reduced.Consequently, the weight of the entire pump can also be reduced.

In addition, when low-temperature fluid is to be compressed, the pistonrod 322 is not subjected to a compressive force. For this reason, thediameter of the piston head 325 can be increased (e.g., diameter of 100mm). In other words, for the known pump where a compressive force isapplied to the piston rod, the diameter of the piston head is limitedto, for example, 40 mm to prevent the piston rod from buckling. For thisreason, the known pump required, for example, five cylinders to achievea sufficient flow volume of low-temperature fluid. For the pumpaccording to the present invention, however, the diameter of the pistonhead 325 can be, for example, 100 mm, and therefore, a sufficient flowvolume can be achieved with a single cylinder.

As a result, for the pump according to the present invention, not onlycan the structure of the pump be simplified, but also the entire pumpcan be made lightweight and compact.

Furthermore, since the cam 313 is in line contact with the rollerbearing 319, the amount of heat entering from the driving source can befurther reduced.

In addition, since the heat-insulating connection section 328 reducesthe amount of heat entering from the rod 320 into the piston rod 322,the amount of heat entering from the driving source can be furtherreduced.

Moreover, even if heat is transmitted (enters) from the rod 320 to thepiston rod 322, heat can be prevented from being transmitted (entering)from the piston rod 322 to the piston main body 324 by the heatinsulator 327.

Furthermore, since the piston main body 324 is provided between thepiston rod 322 and the piston head 325 so that heat from the piston rod322 reaches the piston head 325 via the piston main body 324, the amountof heat input can be further reduced.

Also, since the piston main body 324 has a heat-insulating vacuumstructure that is hollow and vacuumed, the amount of heat input can befurther reduced.

Because of this, the amount of heat input to the piston head 325 can bereduced, and therefore, low-temperature fluid compressed by one endsurface of the piston head 325 can be prevented from being vaporized(boiled off).

Furthermore, the low-temperature-fluid boosting pump 301 according tothis embodiment does not include a component (e.g., piston ring in theknown art) that moves in contact with the inner circumferential surfaceof the compression chamber 326 a. This prevents heat from beinggenerated in the compression chamber 326 a and therefore prevents thelow-temperature fluid from being heated.

A ninth embodiment of a low-temperature-fluid boosting pump according tothe present invention will now be described with reference to FIG. 16.

A low-temperature-fluid boosting pump 402 according to this embodimentdiffers from the pump in the above-described eighth embodiment in thatthe piston head 325 is provided directly at one end portion of thepiston rod 322. The other components are the same as those described inthe above-described embodiment, and hence a description thereof will beomitted.

The same components as those in the above-described eighth embodimentare denoted with the same reference numerals or symbols.

As shown in FIG. 16, in the low-temperature-fluid boosting pump 402according to this embodiment, the length of the piston rod 322 is aboutone-fourth of that in the eighth embodiment, and one end portion of thepiston rod 322 is affixed directly to a through-hole 325 b formed in thecenter of the piston head 325 via the heat insulator 327. For thisreason, in this embodiment, the piston main body 324, the bulkhead 334,and the cylinder 326 that is provided below the bellows 336 in theeighth embodiment are omitted. Therefore, in this embodiment, the lengthof the entire pump in the longitudinal direction (vertical direction inthe figure) is reduced by the length of the omitted components.

Omitting the piston main body 324 and the bulkhead 334 may seem to causea problem in that heat enters from the driving source. In fact, however,as described above, the cam 313 is in line contact with the rollerbearing 319, and furthermore, the end portion 328 a of the rod 320 islinked to the other end portion 328 b of the piston rod 322 in point orline contact through the rolling elements 328 c of the heat-insulatingconnection section 328. Therefore, there is substantially no problem ofheat entering from the driving source.

This embodiment affords an advantage in that the longitudinal length ofa pump unit 412 can be reduced considerably, which allows thelongitudinal length of the entire pump to be reduced and therefore thepump to be made compact.

A tenth embodiment of a low-temperature-fluid boosting pump according tothe present invention will be described with reference to FIG. 17.

A low-temperature-fluid boosting pump 503 according to this embodimentdiffers from the pump in the above-described eighth embodiment in that afirst compression (first-stage compression) is performed with the outercircumferential side of a piston head 525 and a second compression(second-stage compression) is performed with the inner circumferentialside of the piston head 525. The other components are the same as thosedescribed in the above-described embodiment, and hence a descriptionthereof will be omitted.

The same components as those in the above-described eighth embodimentare denoted with the same reference numerals or symbols.

As shown in FIG. 17, according to the low-temperature-fluid boostingpump 503 of this embodiment, a first compression is performed with theouter circumferential side of the piston head 525, a second compressionis performed with the inner circumferential side of the piston head 525,and a drive unit 311 and a low-pressure chamber 534 are provided in acylinder block 523.

A piston 521 in this embodiment includes a piston main body 524 and thepiston head 525, and is reciprocably housed in a cylinder 326 formed inthe cylinder block 523.

The piston head 525 is a member which is ring-shaped in plan view(doughnut), and has a first compressive surface 525 a on one end surface(upper end surface in FIG. 17) adjacent to the outer circumferentialside thereof and a second compressive surface 525 b on one end surfaceadjacent to the inner circumferential side thereof. A low-temperaturefluid (e.g., liquid hydrogen, liquid nitrogen, liquefied carbon dioxide,liquefied natural gas, or liquefied propane gas) is compressed by theseflat compressive surfaces 525 a and 525 b.

Therefore, low-temperature fluid guided from a fluid-suction channel 331through a suction port P1 on the low-pressure side into a compressionchamber 326 a is compressed by the first compressive surface 525 a ofthe piston head 525 for pressure increase to, for example, 5 MPa.Thereafter, the low-temperature fluid flows from a discharge port P2 onthe low-pressure side through a first communication channel (a flowchannel for connecting between the discharge port P2 on the low-pressureside and the low-pressure chamber 534) R1 and is then temporarilyreserved in the low-pressure chamber 534.

The low-temperature fluid reserved in the low-pressure chamber 534 isguided from the low-pressure chamber 534 through a second communicationchannel (flow channel that connects between the low-pressure chamber 534and a suction port P3 on the high-pressure side) into the suction portP3 on the high-pressure side, and is then drawn into the compressionchamber 326 a. The low-temperature fluid drawn into the compressionchamber 326 a is compressed by the second compressive surface 525 b ofthe piston head 525 to increase the pressure to, for example, 30 MPa.Thereafter, the low-temperature fluid is expelled out of the cylinderblock 523 from a discharge port P4 on the high-pressure side via afluid-discharge channel 332. The low-temperature fluid that has beenexpelled out of the cylinder block 523 passes through a pipe 333, istemporarily reserved in a chamber C, and is supplied to a fuel injector,not shown in the figure, through a pipe 335.

According to the low-temperature-fluid boosting pump 503 of thisembodiment, low-temperature fluid is subjected to a pressure increaseto, for example, 5 MPa with the first compressive surface 525 a of thepiston head 525 and is then subjected to another pressure increase withthe second compressive surface 525 b of the piston head 525, up to adesired pressure (e.g., 30 MPa).

In short, this embodiment employs a dual-stage compression techniquewhere low-temperature fluid is temporarily increased to an intermediatepressure and is then further increased to a desired pressure (highpressure), instead of increasing the low-temperature fluid from a lowpressure to a high pressure in one stroke.

By doing so, since the stroke of the piston 521 (i.e., the maximum liftof the cam 313) can be reduced, the longitudinal length of a pump unit512 can be further reduced, which can reduce the longitudinal length ofthe entire pump. This contributes to more compact design of the pump.

In addition, as a result of the stroke of the piston 521 being reduced,the expansion ratio of the bellows 336 and 337 can be decreased (i.e.,the bellows 336 and 337 can be expanded or contracted within a smallerrange). Therefore, the service life of these bellows 336 and 337 can beextended, and accordingly, the reliability of the pump can be improved.

The other effects and advantages are the same as those of theabove-described eighth embodiment, and hence a description thereof willbe omitted.

An eleventh embodiment of a low-temperature-fluid boosting pumpaccording to the present invention will now be described with referenceto FIG. 18.

A low-temperature-fluid boosting pump 604 according to this embodimentdiffers from the pump in the above-described eighth embodiment in that aprecooling layer 630 is provided on an inner side of a heat-insulatingvacuum structure 323 c of a cylinder block 623 which constitutes a pumpunit 612. The other components are the same as those described in theabove-described embodiment, and hence a description thereof will beomitted.

The same components as those in the above-described eighth embodimentare denoted with the same reference numerals or symbols.

As shown FIG. 18, the low-temperature-fluid boosting pump 604 accordingto this embodiment is provided with the precooling layer 630 in the sidewall, the bottom surface, and the top surface of the cylinder block 623.A coolant inlet pipe 631 and a coolant outlet pipe 632 are connected tothis precooling layer 630 so that a coolant (low-temperature fluid suchas liquid hydrogen, liquid nitrogen, liquefied carbon dioxide, liquefiednatural gas, or liquefied propane gas) supplied into the precoolinglayer 630 from the coolant inlet pipe 631 is guided to the outside ofthe cylinder block 623 via the coolant outlet pipe 632.

By providing this precooling layer 630, the entire pump can be cooledsufficiently before the pump is started. This decreases vaporization(boil-off) of low-temperature fluid supplied to thelow-temperature-fluid boosting pump 604.

Furthermore, since this precooling layer 630 also serves as aheat-insulating layer while the pump is being operated, vaporization(boil-off) of the low-temperature fluid can be reduced also while thepump is being operated.

The other effects and advantages are the same as those of theabove-described eighth embodiment, and hence a description thereof willbe omitted.

A twelfth embodiment of a low-temperature-fluid boosting pump accordingto the present invention will now be described with reference to FIG.19.

A low-temperature-fluid boosting pump 705 according to this embodimentdiffers from the pump in the above-described eleventh embodiment in thata bellows 737 is provided in place of the bellows 337. The othercomponents are the same as those described in the above-describedembodiment, and hence a description thereof will be omitted.

The same components as those in the above-described eleventh embodimentare denoted with the same reference numerals or symbols.

As shown in FIG. 19, the bellows (partition) 737 of thelow-temperature-fluid boosting pump 705 according to this embodiment isprovided at a radially inward position of a bellows 336 and in acompression chamber 326 a, which is disposed closer to a piston mainbody 324 (lower side in FIG. 19) than a piston head 325. One end of thebellows 737 is affixed to a surface opposite (the other end surface) theone end surface of the piston head 325, and the other end of the bellows737 is affixed to the top surface of a tongue portion of a bulkhead 334.

Like the above-described bellows 336 and 337, the bellows 737 is madeof, for example, stainless steel or Inconel, which exhibits elasticityat (super) low temperatures.

In this manner, by providing the bellows 737 on the same side as thebellows 336, that is, the side opposite to the one end surface(compressive surface) of the piston head 325, the length of the pump inthe height direction (vertical direction in the figure) can be reduced,and therefore, the entire pump can be made compact.

In addition, since the compressive surface of the piston head 325 canhave a larger area than that in the eleventh embodiment, a larger amountof low-temperature fluid can be compressed at a time. In short, theefficiency (performance) of the pump can be improved.

The other effects and advantages are the same as those of theabove-described eleventh embodiment, and hence a description thereofwill be omitted.

Reference numeral 712 in the figure denotes a pump unit.

A thirteenth embodiment of a low-temperature-fluid boosting pumpaccording to the present invention will be described with reference toFIG. 20.

A low-temperature-fluid boosting pump 806 according to this embodimentdiffers from the pump in the above-described twelfth embodiment in thata bellows 837 is additionally provided. The other components are thesame as those described in the above-described embodiment, and hence adescription thereof will be omitted.

The same components as those in the above-described twelfth embodimentare denoted with the same reference numerals or symbols.

As shown in FIG. 20, the low-temperature-fluid boosting pump 806according to this embodiment is provided with another bellows(partition) 837 adjacent to the other end side (lower side in thefigure) of the bellows 737. This bellows 837 has one end thereof affixedto a lower surface of a tongue portion of a bulkhead 334 and has theother end thereof affixed to an upper surface of the inner wall at theother end portion of a piston main body 324. This bellows 837 separates(partitions) an inner circumferential side (piston rod 322 side) from anouter circumferential side (cylinder block 323 side) in the spacebetween the lower surface of the tongue portion of the bulkhead 334 andthe upper surface of the inner wall at the other end portion of thepiston main body 324.

Like the above-described bellows 336, 337, and 737, the bellows 837 ismade of, for example, stainless steel or Inconel, which exhibitselasticity at (super) low temperatures.

With the bellows 837 provided, the pressure in the space defined by thebellows 837 and the above-described sealing member 341 adjacent to thepiston rod 322 is maintained substantially at atmospheric pressure.Therefore, the difference (pressure difference) between the pressure onthe inner circumferential side and the pressure on the outercircumferential side of the bellows 336, 737, and 837 can be reduced.This allows the service life of these bellows 336, 737, and 837 to beextended. Consequently, the reliability of the pump can be improved.

The other effects and advantages are the same as those of theabove-described eleventh embodiment, and hence a description thereofwill be omitted.

Reference numeral 812 in the figure denotes a pump unit.

A fourteenth embodiment of a low-temperature-fluid boosting pumpaccording to the present invention will be described with reference toFIG. 21.

A low-temperature-fluid boosting pump 907 according to this embodimentdiffers from the pump in the above-described eighth embodiment in that abooster-fluid feeding unit 930 is provided. The other components are thesame as those described in the above-described embodiment, and hence adescription thereof will be omitted.

The same components as those in the above-described eighth embodimentare denoted with the same reference numerals or symbols.

As shown in FIG. 21, the low-temperature-fluid boosting pump 907according to this embodiment is provided with the booster-fluid feedingunit 930. This booster-fluid feeding unit 930 includes a communicatingtube 931 that connects the interior of a chamber C to the interior of acylinder 326 (a space between the lower surface at the other end portionof a piston main body 324, disposed adjacent to the other end side,i.e., the side opposite to a compression chamber 326 a, of the cylinder326, and the bottom surface of the cylinder 326) and a pressureregulator (decompressor) 932 disposed at an intermediate point in thiscommunicating tube 931.

By providing this booster-fluid feeding unit 930, low-temperature fluidwhose pressure has been decreased by the pressure regulator 932 to, forexample, 15 MPa can be supplied to the cylinder 326. Therefore, thedifference between the pressure on the one end surface (compressivesurface) side and the pressure on the other end surface side of a pistonhead 325 can be reduced, and consequently, a bellows with low pressureresistance can be employed.

The other effects and advantages are the same as those of theabove-described thirteenth embodiment, and hence a description thereofwill be omitted.

Reference numeral 912 in the figure denotes a pump unit.

The present invention is not limited to the above-described embodiments.For example, the bellows 336, 337, 737, and 837 can be realized bybellows having cross sections as indicated by solid lines or two-dotchain lines in FIG. 22.

More specifically, convex bellows having one projection towards theoutside in the radial direction, as indicated by the solid lines in FIG.22, or concave bellows having one indentation towards the inside in theradial direction, as indicated by the two-dot chain lines in FIG. 22,can be employed.

Furthermore, the heat-insulating connection sections 128 and 328 are notlimited to those described above. A heat-insulating connection sectionas shown in, for example, FIG. 23 can also be employed.

In a heat-insulating connection section 428 shown in FIG. 23, a heatinsulator 428 c is interposed between an end portion 428 a of across-sectionally T-shaped rod 320 and the other end portion 428 b of across-sectionally T-shaped piston rod 322, and furthermore, theseelements are linked to each other with fasteners J, such as bolts ornuts.

In addition, although a dual-stage compression technique for compressionusing the outer circumferential side and the inner circumferential sideof the piston head 525 has been employed in the embodiment describedwith reference to FIG. 17, the present invention is not limited to thistechnique. Instead, one end surface of the piston head may be furtherdivided in a concentric manner to achieve a three-or-more-stagecompression technique.

Furthermore, it is more preferable that the above-described chamber Cand the low-pressure chamber 534 include a relief valve so thatlow-temperature fluid discharged from this relief valve returns througha return pipe to the suction side of the pump (or a separate fuelbattery, if any fuel battery is provided).

A fifteenth embodiment of a low-temperature-fluid boosting pumpaccording to the present invention will be described with reference toFIG. 24.

As shown in FIG. 24, a low-temperature-fluid boosting pump 1008according to this embodiment includes major components such as a driveunit 1111 and a pump unit 1112 driven by this drive unit 1111.

The drive unit 1111 includes a rod 1115 and a power transmission unit1116 for transmitting a driving force from a driving source (e.g., anelectric motor or an engine), not shown in the figure, to the rod 1115.

The rod 1115 is a circular-cross-section, substantially rod-like memberextending downwards from a lower end surface of the power transmissionunit 1116 and has a heat-insulating connection section 328 at a lowerend portion thereof.

The power transmission unit 1116 causes the rod 1115 to reciprocatelinearly in the vertical direction (as indicated by the arrow in FIG.24) with a stroke of, for example, 2 mm by using a driving force fromthe driving source, not shown in the figure.

The pump unit 1112 includes a piston 1121, a piston rod 1122, and acylinder block 1123.

The piston 1121 includes one linkage member 1124 and one or more (fourin this embodiment) piston heads 1125, and is reciprocably housed in acylinder 1126 formed in the cylinder block 1123.

The linkage member 1124 is a substantially disc-shaped member. One endportion of the piston rod 1122 is linked to a center portion of thelinkage member 1124. In addition, four rods 1127 for linking the lowerend surfaces of the respective piston heads 1125 to the upper endsurface of the linkage member 1124 are provided on the outercircumference of the linkage member 1124. These four rods 1127 arearranged at regular intervals (90°) as shown in FIG. 25.

Each of the piston heads 1125 is a substantially disc-shaped member andis constructed so as to compress a low-temperature fluid (e.g., liquidhydrogen, liquid nitrogen, liquefied carbon dioxide, liquefied naturalgas), liquefied propane gases, etc. by means of one end surface thereof(upper end surface in FIG. 24).

The piston rod 1122 is a circular-cross-section, substantially rod-likemember and has one end portion thereof linked to the upper end surfaceof the linkage member 1124, as described above, and the other endportion thereof connected to an end portion (lower end portion in FIG.24) of the rod 1115 via the heat-insulating connection section 328.

The heat-insulating connection section 328 includes an end portion 328 aof the rod 1115 having a structure similar to the inner race of a rollerbearing; the other end portion 328 b of the piston rod 1122 having astructure similar to the outer race of a roller bearing; and a pluralityof (four in this embodiment) rolling elements (e.g., balls and rollers)328 c disposed between the end portion 328 a of the rod 1115 and theother end portion 328 b of the piston rod 1122.

By doing so, the end portion 328 a of the rod 1115 and the other endportion 328 b of the piston rod 1122 are linked to each other in pointor line contact via the rolling elements 328 c. This significantlyreduces the amount of heat being transmitted (entering) from the rod1115 to the piston rod 1122.

In addition, since the piston rod 1122 is designed to have a maximumpossible length, even if heat is transmitted (enters) from the rod 1115to the piston rod 1122, the amount of heat being transmitted (entering)from the piston rod 1122 to the linkage member 1124 is minimized.

A through-hole 323 a through which the rod 1115 passes is formed in thetop center of the cylinder block 1123. An inner space 329 communicatingwith the through-hole 323 a is formed inside the top portion of thecylinder block 1123. The heat-insulating connection section 328 isaccommodated in this inner space 329.

Furthermore, in the cylinder block 1123 below this inner space 329, thecylinder 1126 communicating with the inner space 329 via a through-hole1123 b through which the piston rod 1122 passes is formed in thelongitudinal direction (vertical direction in FIG. 24). One end (upperside in FIG. 24) of the cylinder 1126 constitutes compression chambers1126 a each having an inner diameter larger than the outer diameter ofthe piston head 1125. The piston heads 1125 are accommodated in thesecompression chambers 1126 a, respectively.

As indicated by reference symbol 1123 c, the interiors of the side wall,the bottom surface, and the top surface of the cylinder block 1123 arehollow and vacuumed to achieve a heat-insulating vacuum structure.

On the other hand, a suction port 1123 d and a discharge port 1123 ecommunicating with a compression chamber 1126 a are provided at aposition that faces the center of one end surface of the correspondingpiston head 1125 in the cylinder block 1123, disposed between thecompression chamber 1126 a and the inner space 329. The suction port1123 d and the discharge port 1123 e are each provided with a ball checkvalve 1130 to control suction and discharge of low-temperature fluid.

Each suction port 1123 d is provided so as to communicate with afluid-suction channel 1131 formed in the cylinder block 1123, whereaseach discharge port 1123 e is provided so as to communicate with afluid-discharge channel 1132 formed in the cylinder block 1123.Therefore, low-temperature fluid guided from the fluid-suction channel1131 via each suction port 1123 d into the compression chamber 1126 a iscompressed by one end surface of the piston head 1125 so that thepressure is increased to, for example, 30 MPa. Thereafter, thelow-temperature fluid is guided out of the cylinder block 1123 from thedischarge port 1123 e via the fluid-discharge channel 1132.

The low-temperature fluid that has been guided out of the cylinder block1123 via the fluid-discharge channel 1132 is temporarily stored(reserved) in a chamber 1134 via a pipe 1133. The low-temperature fluidreserved in the chamber 1134 is guided into a heat exchanger 1136through a pipe 1135 and then vaporized. Most of the low-temperaturefluid is supplied to a fuel injector, not shown in the figure, through apipe 1137, whereas part of the low-temperature fluid is guided through apipe 1138 and a pressure regulator (decompressor) 1139 into the cylinder1126 (a space between the lower surface at the other end portion of thelinkage member 1124, disposed adjacent to the other end side, i.e., theside opposite to the compression chambers 1126 a, of the cylinder 1126,and the bottom surface of the cylinder 1126).

Low-temperature fluid whose pressure has been increased to, for example,30 MPa is reserved in the chamber 1134.

In addition, vaporized low-temperature fluid whose pressure has beendecreased to, for example, 15 MPa by the pressure regulator 1139 issupplied into the cylinder 1126.

Each compression chamber 1126 a has a bellows (partition) 1140 therein.This bellows 1140 partitions (separates) an inner circumferential side(rod 1127 side) from an outer circumferential side (cylinder block 1123side) of the corresponding compression chamber 1126 a, which is disposedcloser to the linkage member 1124 (lower side in FIG. 24) than thepiston head 1125. One end of the bellows 1140 is affixed to a surfaceopposite (the other end surface) one end surface of the piston head1125, and the other end of the bellows 1140 is affixed to the inner wallsurface of the cylinder block 1123.

Furthermore, a bellows (partition) 1141 is also provided at an outwardposition in the radial direction at one end portion of the piston rod1122. This bellows 1141 partitions (separates) an inner circumferentialside (adjacent to the piston rod 1122) from an outer circumferentialside (adjacent to the cylinder block 1123) of the piston rod 1122 at oneend portion thereof. One end of the bellows 1141 is affixed to the upperend surface of the linkage member 1124, and the other end of the bellows1141 is affixed to the inner wall surface of the cylinder block 1123.

These bellows 1140 and 1141 are made of, for example, stainless steel orInconel, which exhibits elasticity at (super) low temperatures.

Reference numerals 1142, 1143, and 1144 in FIG. 24 each denote a(heat-insulating) sealing member which is ring-shaped in plan view.

FIG. 25 is a cross-sectional view taken along line XXV-XXV of FIG. 24.

With the above-described structure, when the rod 1115 of the drive unit1111 reciprocates linearly in the vertical direction, the piston rod1122 linked to the rod 1115 through the heat-insulating connectionsection 328 reciprocates linearly in the vertical direction togetherwith the piston 1121, the low-temperature fluid supplied from thesuction ports 1123 d is compressed by one end surface of each pistonhead 1125 so that the pressure is increased, and then thelow-temperature fluid is expelled from the discharge port 1123 e via thefluid-discharge channel 1132 to the outside of the cylinder block 1123.

According to the low-temperature-fluid boosting pump 1008 of thisembodiment, as a result of the piston rod 1122 being pulled towards thedrive unit 1111 (upward in FIG. 24), low-temperature fluid is compressedby one end surface of each piston head 1125. In other words, whenlow-temperature fluid is to be compressed, no compressive force isapplied to the piston rod 1122.

As a result, the diameter of the piston rod 1122 can be reduced comparedwith a piston rod in the known art, which is subjected to a compressiveforce. Therefore, not only can the amount of heat entering from adriving source be reduced, but also the weight of the piston rod 1122can be reduced. Consequently, the weight of the entire pump can also bereduced.

Furthermore, since there is no component (e.g., piston ring in the knownart) that moves in contact with the inner circumferential surfaces ofthe compression chambers 1126 a, heat is prevented from being generatedin the compression chambers 1126 a, and therefore, low-temperature fluidis prevented from being heated.

In addition, each bellows 1140 completely partitions (separates) aninner circumferential side (inward position in the radial direction)from an outer circumferential side (outward position in the radialdirection) of the corresponding compression chamber 1126 a. Therefore,low-temperature fluid can be prevented from leaking from the innercircumferential side of the compression chamber 1126 a to the outercircumferential side of the compression chamber 1126 a (or from theouter circumferential side of the compression chamber 1126 a to theinner circumferential side of the compression chamber 1126 a). Thisimproves the compression efficiency of the low-temperature-fluidboosting pump 1008. Furthermore, since low-temperature fluid that isvaporized by the heat exchanger 1136 and subjected to pressureadjustment to a predetermined pressure (e.g., 15 MPa) by the pressureregulator 1139 exists outside each bellows 1140 (outward position in theradial direction), deformation of the bellows 1140 can be reduced whenlow-temperature fluid drawn into the bellows 1140 is to be compressed.This extends the service life of the bellows 1140 and increases thereliability of the low-temperature-fluid boosting pump 1008.

In addition, the heat-insulating connection section 328 reduces theamount of heat entering from the rod 1115 to the piston rod 1122,thereby further reducing the amount of heat entering from the drivingsource.

Furthermore, because the linkage member 1124 is provided between thepiston rod 1122 and the piston heads 1125, heat from the piston rod 1122reaches the piston heads 1125 through the linkage member 1124. This canfurther reduce the amount of input heat.

In addition, since the rod 1115 connecting to the power transmissionunit 1116 extends to the side where the suction ports 1123 d and thedischarge ports 1123 e are disposed (upper side in FIG. 24), not onlycan the length of the pump unit 1112 in the longitudinal direction(axial direction) be reduced, but also the length of the entire pump inthe longitudinal direction (axial direction) can be reduced. Thiscontributes to compact and lightweight design of the pump.

A sixteenth embodiment of a low-temperature-fluid boosting pumpaccording to the present invention will be described with reference toFIG. 26.

A low-temperature-fluid boosting pump 2009 according to this embodimentis a so-called swash plate (or swash) pump. The low-temperature-fluidboosting pump 2009 includes major components such as a drive unit 2161and a pump unit 2162 that is driven by this drive unit 2161.

The same components as those in the above-described fifteenth embodimentare denoted with the same reference numerals or symbols.

The drive unit 2161 includes a rod 2165 and a power transmission unit2166 that transmits a driving force from a driving source (e.g., anelectric motor or an engine), not shown in the figure, to the rod 2165.

The rod 2165 is a substantially rod-like member having a circular crosssection, extending downwards from the lower end surface of the powertransmission unit 2166.

The power transmission unit 2166 rotates the rod 2165 in one direction(direction indicated by the arrow in FIG. 26) using a driving force froma driving source, not shown in the figure.

The pump unit 2162 includes one or more (four in this embodiment)pistons 2171, a swash plate (also called a “yoke”) 2172, and a cylinderblock 2173.

Each piston 2171 is a circular-cross-section, substantially rod-likemember having a piston head 2171 a at one end portion thereof and apiston shoe 2171 b at the other end portion thereof. Each piston 2171 isreciprocably housed in the cylinder 2176.

The piston head 2171 a is a so-called large-diameter portion that has anouter diameter larger than the outer diameter of a piston rod 2171 cthat links this piston head 2171 a and the piston shoe 2171 b, and (forexample, liquid hydrogen, liquid nitrogen, liquefied carbon dioxide,liquefied natural gas), liquefied propane gas, etc. is compressed by oneflat end surface (upper end surface in FIG. 26) of this piston head 2171a.

Like the piston head 2171 a, the piston shoe 2171 b is also a so-calledlarge-diameter portion that has an outer diameter larger than the outerdiameter of the piston rod 2171 c. One end surface (lower surface inFIG. 26) of the piston shoe 2171 b slides along a sliding surface P ofthe swash plate 2172 having a tilt angle.

The cylinder block 2173 contains the same number of compression chambers1126 a as that of the pistons 2171, and the compression chambers 1126 aare formed along a longitudinal direction (vertical direction in FIG.26). Each compression chamber 1126 a accommodates one piston head 2171a.

As shown in FIG. 26, the piston shoes 2171 b and the swash plate 2172are housed adjacent to the other end side (lower side in FIG. 26) of thecylinder 2176.

Furthermore, a through-hole 1123 a through which the rod 2165 passes isformed in the center of the cylinder block 2173. In addition, theinteriors of the side wall, the bottom surface, and the top surface ofthe cylinder block 2173 constitute a heat-insulating vacuum structurethat is hollow and vacuumed, as shown by reference symbol 1123 c.

On the other hand, a suction port 1123 d and a discharge port 1123 ecommunicating with a compression chamber 1126 a are provided at aposition that faces the center of one end surface of the correspondingpiston head 2171 a, i.e., at a top portion in the cylinder block 2173.The suction port 1123 d and the discharge port 1123 e are each providedwith a ball check valve 1130 to control suction and discharge oflow-temperature fluid.

Each suction port 1123 d is provided so as to communicate with afluid-suction channel 1131 formed in the cylinder block 2173, whereaseach discharge port 1123 e is provided so as to communicate with afluid-discharge channel 1132 formed in the cylinder block 2173.Therefore, a low-temperature fluid guided from the fluid-suction channel1131 via each suction port 1123 d into the compression chamber 1126 a iscompressed by one end surface of the piston head 2171 a so that thepressure is increased to, for example, 30 MPa. Thereafter, thelow-temperature fluid is guided out of the cylinder block 2173 from thedischarge port 1123 e via the fluid-discharge channel 1132.

The low-temperature fluid that has been guided out of the cylinder block2173 via the fluid-discharge channel 1132 is temporarily stored(reserved) in a chamber 1134 via a pipe 1133. The low-temperature fluidreserved in the chamber 1134 is guided into a heat exchanger 1136through a pipe 1135 and then vaporized. Most of the low-temperaturefluid is supplied to a fuel injector, not shown in the figure, through apipe 1137, whereas part of the low-temperature fluid is guided through apipe 1138 and a pressure regulator (decompressor) 1139 into thecompression chambers 1126 a (i.e., a space adjacent to the other endsurface of each piston head 2171 a, located opposite to a bellows 1140).

Low-temperature fluid whose pressure has been increased to, for example,30 MPa is reserved in the chamber 1134.

In addition, vaporized low-temperature fluid whose pressure has beendecreased to, for example, 15 MPa by the pressure regulator 1139 issupplied into the compression chambers 1126 a.

Each compression chamber 1126 a has the bellows (partition) 1140therein. This bellows 1140 partitions (separates) an innercircumferential side (piston rod 2171 c side) from an outercircumferential side (cylinder block 2173 side) of the correspondingcompression chamber 1126 a, which is disposed closer to the piston shoe2171 b (lower side in FIG. 26) than the piston head 2171 a. One end ofthe bellows 1140 is affixed to a surface opposite (the other endsurface) one end surface of the piston head 2171 a, and the other end ofthe bellows 1140 is affixed to the inner wall surface of the cylinderblock 2173.

Furthermore, a bellows (partition) 2180 is also provided at an outwardposition in the radial direction at one end portion of each piston rod2171 c. This bellows 2180 partitions (separates) an innercircumferential side (adjacent to the piston rod 2171 c) from an outercircumferential side (adjacent to the cylinder block 2173) of thecorresponding piston rod 2171 c at one end portion thereof. One end ofthe bellows 2180 is affixed to an outer circumferential end portion onthe other end surface (upper surface in FIG. 26) of the piston shoe 2171b, and the other end of the bellows 2180 is affixed to the inner wallsurface of the cylinder block 2173.

These bellows 1140 and 2180 are made of, for example, stainless steel orInconel, which exhibits elasticity at (super) low temperatures.

Reference numerals 1142, 1143, and 1144 in FIG. 26 each denote a(heat-insulating) sealing member which is ring-shaped in plan view.Reference numerals 2181 and 2182 each denote a thrust roller bearing.

With the above-described structure, when the rod 2165 is rotated by thedriving source (in one direction), the piston shoes 2171 b slide alongthe sliding surface P by means of the thrust bearings 2181, andfurthermore, the pistons 2171 are caused to reciprocate in the cylinder2176, thereby successively compressing low-temperature fluid flowinginto the compression chambers 1126 a. In this embodiment, the strokes ofthe pistons 2171 are set to, for example, 2 mm.

According to the low-temperature-fluid boosting pump 2009 of thisembodiment, as a result of the rod 2165 being rotated in one direction(as indicated by the arrow in FIG. 26), low-temperature fluid iscompressed by one end surface of each piston head 2171 a. In otherwords, when low-temperature fluid is to be compressed, no compressiveforce is applied to the rod 2165.

As a result, the diameter of the rod 2165 can be reduced compared withthe type of piston rod used in the known art, which is subjected to acompressive force. Therefore, not only can the amount of heat enteringfrom a driving source be reduced, but also the weight of the rod 2165can be reduced. Consequently, the weight of the entire pump can also bereduced.

Furthermore, since there is no component (e.g., piston ring in the knownart) that moves in contact with the inner circumferential surfaces ofthe compression chambers 1126 a, heat is prevented from being generatedin the compression chambers 1126 a, and therefore, low-temperature fluidis prevented from being heated.

In addition, each bellows 1140 completely partitions (separates) aninner circumferential side (inward position in the radial direction)from an outer circumferential side (outward position in the radialdirection) of the corresponding compression chamber 1126 a. Therefore,low-temperature fluid can be prevented from leaking from the innercircumferential side of the compression chamber 1126 a to the outercircumferential side of the compression chamber 1126 a (or from theouter circumferential side of the compression chamber 1126 a to theinner circumferential side of the compression chamber 1126 a). Thisimproves the compression efficiency of the low-temperature-fluidboosting pump 2009. Furthermore, since low-temperature fluid that isvaporized by the heat exchanger 1136 and is subjected to pressureadjustment to a predetermined pressure (e.g., 15 MPa) by the pressureregulator 1139 exists outside each bellows 140 (outward position in theradial direction), deformation of the bellows 1140 can be reduced whenthe low-temperature fluid drawn into the bellows 1140 is to becompressed. This extends the service life of the bellows 1140 andincreases the reliability of the low-temperature-fluid boosting pump2009.

In addition, since the rod 2165 connecting to the power transmissionunit 2166 extends to the side where the suction ports 1123 d and thedischarge ports 1123 e are disposed (upper side in FIG. 26), not onlycan the length of the pump unit 2162 in the longitudinal direction(axial direction) be reduced, but also the length of the entire pump inthe longitudinal direction (axial direction) can be reduced. Thiscontributes to compact and lightweight design of the pump.

Although a four-cylinder structure provided with four pistons and fourcylinders has been described in the above-described embodiment, thepresent invention is not limited to this structure. For example, asingle-cylinder, two-cylinder, three-cylinder, or five-or-more-cylinderstructure is also acceptable.

Furthermore, the thrust roller bearing 2182 described in the sixteenthembodiment is not limited to the type of bearing that supports the swashplate 2172 at a single point in the center on the bottom surface of theswash plate 2172, as shown in FIG. 26. Instead, the entire bottomsurface of the swash plate 2172 can be supported with two or more thrustroller bearings disposed in the circumferential direction.

In addition, it is preferable that the angle of this swash plate 2172 bevariable using, for example, an actuator. In other words, avariable-capacity structure is preferable. By doing so, the amount ofdischarge of the pump can be changed simply by changing the angle of theswash plate 2172, i.e., without changing the number of revolutions fordriving the pump.

Furthermore, although each of the suction port 1123 d and the dischargeport 1123 e is provided with the ball check valve 1130 in theabove-described embodiment, the present invention is not limited to thisstructure. Instead, a forcible drive system as seen with, for example, aDOHC of an internal-combustion engine is also acceptable. Furthermore, astructure with a reed valve, a poppet valve, etc. can also be used.

In addition, the present invention is not limited to the above-describedembodiments. For example, the bellows 1140, 1141, and 2180 can berealized by bellows having cross sections as indicated by solid lines ortwo-dot chain lines in FIG. 22.

More specifically, convex bellows having one projection towards theoutside in the radial direction, as indicated by the solid lines in FIG.22, or concave bellows having one indentation towards the inside in theradial direction, as indicated by the two-dot chain lines in FIG. 22,can be employed.

Furthermore, the heat-insulating connection section 328 shown in FIG. 24is not limited to that described above. A heat-insulating connectionsection as shown in, for example, FIG. 23 can also be employed.

Furthermore, it is more preferable that the above-described chamber 1134include a relief valve so that low-temperature fluid discharged fromthis relief valve returns through a return pipe to the suction side ofthe pump (or a separate fuel battery, if any fuel battery is provided).

Furthermore, the drive unit 311 according to the eighth to fourteenthembodiments is not limited to a cam-driven drive unit as shown in thefigures. The drive unit 311 can be realized by, for example, acrank-driven drive unit where the rod 320 is forcibly driven.

In addition, it is more preferable that, in the fifteenth and sixteenthembodiments, the piston rod 1122 be linked (connected) to the linkagemember 1124 and the rod 2165 be linked (connected) to the swash plate2172 through the heat insulator 327 described in the eighth tofourteenth embodiments.

Moreover, in each of the above-described eighth to fifteenthembodiments, it is more preferable that a guiding member be provided,for example, between the piston rods 322 and 1122 and the cylinderblocks 323 and 1123, between the piston main bodies 324 and 524 and thecylinder 326, or between the linkage member 1124 and the cylinder 1126,so that the piston main bodies, the piston heads, etc. that are housedin the cylinders and reciprocate in the cylinders do not interfere withthe inner wall surfaces of the cylinders (cylinder walls).

Examples of such a guiding member include a linear bearing disposedbetween the piston rods 322 and 1122 and cylinder blocks 323 and 1123,between the outer circumferential surfaces of the piston main bodies 324and 524 and the inner wall surface of the cylinder 326, or between theouter circumferential surface of the linkage member 1124 and the innerwall surface of the cylinder 1126, a member that guides a cylindricalprotrusion protruding downwards from the lower end surfaces of thepiston main bodies 324 and 524 into a cylindrical indentation (dent)formed in the centers of the bottom surfaces of the cylinders 326 and1126, and so forth.

By doing so, reciprocating members such as the piston main bodies andthe piston heads perform reciprocal movement in the cylinders withoutwobbling or vibrating. This can prevent such reciprocating members frominterfering with the inner wall surfaces of the cylinders, andfurthermore, allows the reciprocating members to be driven smoothly withminimum driving force.

In addition, in each of the above-described fourteenth to sixteenthembodiments, spaces receiving vaporized low-temperature fluid in theseembodiments can be vacuumed.

By doing so, not only is an increase in the temperature of the cylinderblocks suppressed, but also an increase in the temperature oflow-temperature fluid flowing into the compression chambers issuppressed.

In this case, the pipes 931 and 1138 and the pressure regulator 1139shown in FIGS. 21, 24, and 26 are omitted.

Furthermore, in the above-described embodiments, it is more preferablethat an vacuumed space be formed between the piston rods 322 and 1122and the cylinder blocks 323 and 1123.

For example, in the fifteenth embodiment shown in FIG. 24, a bellows(same as the bellows 1141) for separating a space adjacent to the innercircumferential side from a space adjacent to the outer circumferentialside of the piston rod 1122 is provided between the lower surface of theother end portion 328 b of the piston rod 1122 and the upper surface ofthe bottom of the inner space 329.

More specifically, the space between the cylinder block 1123 and thepiston rod 1122 is vacuumed to prevent heat from the piston rod 1122(i.e., heat moving from the driving source 1111 side to the piston rod1122 side) from being transmitted to the cylinder block 1123.

By doing so, not only is an increase in the temperature of the cylinderblock 1123 suppressed, but also an increase in the temperature oflow-temperature fluid flowing into the compression chambers 1126 a issuppressed.

In the current description, the term “low temperature” designatestemperatures of about −273° C. to 0° C., and the term “high pressure”designates pressures of about 0.2 MPa to 200 MPa.

The word “fluid” used in the current description includes “liquid,”“gas,” and “colloid.”

1. A booster pump comprising: a piston having a piston head and a pistonrod; and a cylinder having a compression chamber that accommodates thepiston head so that a fluid is compressed by one end surface of thepiston head, wherein the piston head is provided with a bellows forseparating a space adjacent to the piston rod from a space adjacent tothe cylinder in the compression chamber.
 2. The booster pump accordingto claim 1, wherein a filler filling a space between an outer surface ofthe bellows and an inner circumferential surface of the cylinder isprovided.
 3. The booster pump according to claim 1, wherein aring-shaped sealing member is provided at one end portion, adjacent tothe piston head, of the bellows.
 4. The booster pump according to claim1, wherein the piston rod has a heat-insulating vacuum structure that ishollow and vacuumed.
 5. A booster comprising at least two of the boosterpumps according to claim 1, wherein multistage compression is performedwith the booster pumps.
 6. A low-temperature-fluid storage tank forstoring a low-temperature fluid in a low-temperature state, comprising:the booster pump according to claim 1; a low-temperature-fluid reservoirreserving the low-temperature fluid; and a low-temperature container foraccommodating the booster pump or the booster and thelow-temperature-fluid reservoir.
 7. The low-temperature-fluid storagetank according to claim 6, wherein the booster pump or the booster isdisposed downstream of the low-temperature-fluid reservoir and outsidethe low-temperature-fluid reservoir.
 8. The low-temperature-fluidstorage tank according to claim 6, wherein a low-temperature slush fluidin a solid/liquid two-phase state is reserved in thelow-temperature-fluid reservoir.
 9. The low-temperature-fluid storagetank according to claim 8, wherein a mesh is provided at an outlet ofthe low-temperature-fluid reservoir.
 10. The low-temperature-fluidstorage tank according to claim 9, wherein a heater is provided in thelow-temperature-fluid reservoir.
 11. The low-temperature-fluid storagetank according to claim 6, wherein a heat exchanger is disposeddownstream of the booster pump or the booster.
 12. Thelow-temperature-fluid storage tank according to claim 6, wherein aradiation shield plate is provided on an inner surface of thelow-temperature container.
 13. A low-temperature-fluid boosting pumpcomprising a cylinder block having therein a compression chamber; and apiston head that is accommodated in the compression chamber andreciprocates in the compression chamber so that a low-temperature fluidis compressed by one end surface of the piston head, wherein a flexiblepartition for separating a space adjacent to an inner circumferentialside from a space adjacent to an outer circumferential side of thepiston head is provided between the one end surface of the piston headand an inner surface of the compression chamber which faces the one endsurface.
 14. The low-temperature-fluid boosting pump according to claim13, wherein a pressure-boosted fluid resides on an outer side of thepartition.
 15. The low-temperature-fluid boosting pump according toclaim 13, wherein an outer side of the partition is vacuumed.
 16. Alow-temperature-fluid boosting pump comprising: a piston rod driven by adrive unit connected to a driving source; a piston head that isconnected to the piston rod and reciprocates with the piston rod; and acylinder having a compression chamber that accommodates the piston headso that a low-temperature fluid is compressed by one end surface of thepiston head, wherein the drive unit is disposed adjacent to the one endsurface of the piston head, and a shank of the piston rod is subjectedto a tensile force in a direction substantially equal to a direction inwhich the shank extends when the low-temperature fluid is to becompressed.
 17. The low-temperature-fluid boosting pump according toclaim 16, wherein the piston head is divided into at least twoconcentric subsections to achieve a multistage compression structurewhere the low-temperature fluid is gradually increased to a desiredpressure by sequentially passing through the one end surface of thedivided piston head.
 18. The low-temperature-fluid boosting pumpaccording to claim 16, wherein a flexible partition for separating aspace adjacent to the piston rod from a space adjacent to the cylinderin the compression chamber is provided adjacent to the one end surfaceand adjacent to the other end surface of the piston head.
 19. Thelow-temperature-fluid boosting pump according to claim 16, wherein aflexible partition for separating a space adjacent to the piston rodfrom a space adjacent to the cylinder in the compression chamber isprovided adjacent to the other end surface of the piston head.
 20. Thelow-temperature-fluid boosting pump according to claim 16, wherein aprecooling layer is formed in the cylinder.
 21. Thelow-temperature-fluid boosting pump according to claim 16, wherein thedrive unit is linked to the piston rod via a heat-insulating connectionsection.
 22. The low-temperature-fluid boosting pump according to claim16, wherein the piston head is linked to the piston rod via a heatinsulator.
 23. The low-temperature-fluid boosting pump according toclaim 16, wherein a guiding member for guiding the shank of the pistonrod is provided between a cylinder block and the piston rod.
 24. Thelow-temperature-fluid boosting pump according to claim 16, wherein aspace between a cylinder block and the shank of the piston rod is avacuum.
 25. The low-temperature-fluid boosting pump according to claim16, wherein the cylinder is immersed in low-temperature fluid stored ina low-temperature-fluid storage tank and is attachable to and detachablefrom the low-temperature-fluid storage tank.
 26. Thelow-temperature-fluid boosting pump according to claim 16, wherein thedrive unit and the cylinder are immersed in low-temperature fluid storedin a low-temperature-fluid storage tank and are attachable to anddetachable from the low-temperature-fluid storage tank.
 27. Alow-temperature-fluid feeder comprising: the low-temperature-fluidboosting pump according to claim 16; a chamber for reserving alow-temperature fluid whose pressure has been increased by thelow-temperature-fluid boosting pump; and a fuel injector supplied withthe low-temperature fluid from the chamber.
 28. Thelow-temperature-fluid feeder according to claim 27, wherein abooster-fluid feeding unit for liquefying or vaporizing thelow-temperature fluid in the chamber and supplying the low-temperaturefluid into the cylinder disposed adjacent to the other end surface ofthe piston head of the low-temperature-fluid boosting pump is provided.29. The low-temperature-fluid feeder according to claim 27, wherein aheat exchanger for vaporizing liquid hydrogen is provided between thechamber and the fuel injector, and a booster-fluid feeding unit foradjusting the pressure of the vaporized hydrogen and supplying thehydrogen into the cylinder disposed adjacent to the other end surface ofthe piston head of the low-temperature-fluid boosting pump is provided.30. The low-temperature-fluid feeder according to claim 27, wherein thechamber is provided with a relief valve.
 31. A low-temperature-fluidboosting pump comprising a cylinder block having therein a compressionchamber; and a piston head that is accommodated in the compressionchamber and reciprocates in the compression chamber so that alow-temperature fluid is compressed by one end surface of the pistonhead, wherein a flexible partition for separating a space adjacent to aninner circumferential side from a space adjacent to an outercircumferential side in the compression chamber is provided adjacent tothe other end surface of the piston head.
 32. The low-temperature-fluidboosting pump according to claim 31, wherein a pressure-boosted fluidresides on an inner side of the partition.
 33. The low-temperature-fluidboosting pump according to claim 31, wherein an inner side of thepartition is vacuumed.
 34. The low-temperature-fluid boosting pumpaccording to claim 16, wherein a guiding member for guiding the pistonhead is provided between the cylinder block and the piston head.
 35. Thelow-temperature-fluid boosting pump according to claim 13, wherein thecylinder block is immersed in low-temperature fluid stored in alow-temperature-fluid storage tank and is attachable to and detachablefrom the low-temperature-fluid storage tank.
 36. Thelow-temperature-fluid boosting pump according to claim 31, wherein aguiding member for guiding the piston head is provided between thecylinder block and the piston head.
 37. The low-temperature-fluidboosting pump according to claim 31, wherein the cylinder block isimmersed in low-temperature fluid stored in a low-temperature-fluidstorage tank and is attachable to and detachable from thelow-temperature-fluid storage tank.
 38. The low-temperature-fluidboosting pump according to claim 34, wherein the cylinder block isimmersed in low-temperature fluid stored in a low-temperature-fluidstorage tank and is attachable to and detachable from thelow-temperature-fluid storage tank.